Convert README to adoc, add CHANGELOG & Priorities

CONTRIBUTING.adoc

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+[[contributing-to-the-git-client-plugin]]
+= Contributing to the Git Client Plugin
+
+The git client plugin implements the https://plugins.jenkins.io/scm-api[Jenkins SCM API].
+Refer to the SCM API documentation for https://github.com/jenkinsci/scm-api-plugin/blob/master/docs/implementation.adoc#naming-your-plugin[plugin naming conventions]
+and for the https://github.com/jenkinsci/scm-api-plugin/blob/master/CONTRIBUTING.md#add-to-core-or-create-extension-plugin[preferred locations of new functionality].
+
+Plugin source code is hosted on https://github.com/jenkinsci/git-client-plugin[GitHub].
+New feature proposals and bug fix proposals should be submitted as https://help.github.com/articles/creating-a-pull-request[GitHub pull requests].
+Your pull request will be evaluated by the https://ci.jenkins.io/job/Plugins/job/git-client-plugin/[Jenkins job].
+
+Before submitting your change, please assure that you've added tests which verify your change.
+There have been many developers involved in the git client plugin and there are many, many users who depend on the git client plugin.
+Tests help us assure that we're delivering a reliable plugin, and that we've communicated our intent to other developers as executable descriptions of plugin behavior.
+
+Code coverage reporting is available as a maven target.
+Please improve code coverage with tests when you submit.
+
+* `mvn -P enable-jacoco clean install jacoco:report` to report code coverage
+
+Please don't introduce new spotbugs output.
+
+* `mvn spotbugs:check` to analyze project using https://spotbugs.github.io/[Spotbugs].
+* `mvn spotbugs:gui` to review Spotbugs report using GUI
+
+Code formatting in the git client plugin varies between files.
+Try to maintain reasonable consistency with the existing files where feasible.
+Please don't perform wholesale reformatting of a file without discussing with the current maintainers.
+New code should follow the https://github.com/jenkinsci/scm-api-plugin/blob/master/CONTRIBUTING.md#code-style-guidelines[SCM API code style guidelines].
+
+[[pull-request-review]]
+== Reviewing Pull Requests
+
+Maintainers triage pull requests by reviewing them and by assigning labels.
+Release drafter uses the labels to automate link:https://github.com/jenkinsci/git-client-plugin/releases[release notes].
+link:Priorities.adoc#git-client-plugin-development-priorities[Prioritization] uses the labels to group relevant pull requests.
+
+Others are encouraged to review pull requests, test pull request builds, and report their results in the pull request.
+Refer to the link:Priorities.adoc#priorities[maintainer's priority list] for topics the plugin maintainers are considering.
+
+=== Testing a Pull Request Build
+
+Pull request builds merge the most recent changes from their target branch with the change proposed in the pull request.
+They can be downloaded from ci.jenkins.io and used to test the pull request.
+Steps to test a pull request build are:
+
+. *Find the pull request on link:https://github.com/jenkinsci/git-client-plugin/pulls[GitHub]* - for example, link:https://github.com/jenkinsci/git-client-plugin/pull/467[pull request 467]
+. *Find the link:https://ci.jenkins.io/job/Plugins/job/git-client-plugin/view/change-requests/[ci.jenkins.io] artifacts for that pull request* from the link to the link:https://ci.jenkins.io/job/Plugins/job/git-client-plugin/job/PR-676/lastSuccessfulBuild/[artifacts in the Jenkins job] in "*Show all checks*"
+. *Download the `hpi` file* (like `git-client-3.0.1-rc3444.b3d767e3d46a.hpi`) to your computer
+. *Upload the `hpi` file* to Jenkins from the Jenkins Plugin Manager
+. *Restart your Jenkins* and you're ready to test
+
+[[bug-triage]]
+== Reviewing Bug Reports
+
+Git client plugin bug reports are assigned to one of the maintainers by default.
+link:https://issues.jenkins-ci.org/issues/?jql=project%20%3D%20JENKINS%20AND%20status%20in%20(Open)%20AND%20component%20%3D%20git-client-plugin%20and%20assignee%20in%20(rsandell%2Cmarkewaite%2Cfcojfernandez)[Open bug reports] assigned to a maintainer are assumed to have not been reviewed.
+When a maintainer completes review of an issue, they include a comment on the bug report and set the 'Assignee' to 'Unassigned'.
+
+Others are welcome to review bug reports, comment on the results of the review, and set the 'Assignee' to 'Unassigned'.
+Typical bug review tasks include:
+
+* Review summary and description
+* Attempt to duplicate the issue
+* Add a comment with results of the attempt to duplicate the issue

Priorities.adoc

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+[[git-client-plugin-development-priorities]]
+= Git Client Plugin Development Priorities
+
+[[introduction]]
+== Introduction
+
+The maintainers of this plugin use this file to list the work areas which are receiving more attention from them.
+Higher priority items will generally receive more attention from maintainers than lower priority items.
+Others are encouraged to help with the plugin in areas of their own interest.
+When others provide additional help on an item, it tends to raise the priority of the item.
+
+== Priorities
+
+. link:CONTRIBUTING.adoc#bug-triage[Bug report triage]
+. link:https://github.com/jenkinsci/git-client-plugin/pulls?utf8=%E2%9C%93&q=is%3Apr+is%3Aunmerged+label%3AShortTerm[Short term improvements]
+. link:https://github.com/jenkinsci/git-client-plugin/pulls?utf8=%E2%9C%93&q=is%3Apr+is%3Aunmerged+label%3ACaching[Caching and performance improvements]
+. link:https://github.com/jenkinsci/git-client-plugin/pulls?utf8=%E2%9C%93&q=is%3Apr+is%3Aunmerged+label%3AnotifyCommit[notifyCommit and webhook improvements]
+. link:https://github.com/jenkinsci/git-client-plugin/pulls?utf8=%E2%9C%93&q=is%3Apr+is%3Aunmerged+label%3AChangelog+[Changelog improvements]
+. link:https://github.com/jenkinsci/git-client-plugin/pulls?utf8=%E2%9C%93&q=is%3Apr+is%3Aunmerged+label%3ASubmodules[Submodule improvements]
+. link:https://github.com/jenkinsci/git-client-plugin/pulls?utf8=%E2%9C%93&q=is%3Apr+is%3Aunmerged+label%3ABuildData[BuildData memory bloat]
+
+[[bug-reports]]
+== Bug Reports
+
+Report issues and enhancements in the https://issues.jenkins-ci.org[Jenkins issue tracker].
+link:CONTRIBUTING.adoc#bug-triage[Review bug reports] and provide comments to submitters.
+
+[[contributing-to-the-plugin]]
+== Contributing to the Plugin
+
+Refer to link:CONTRIBUTING.adoc#contributing-to-the-git-client-plugin[contributing to the plugin] for contribution guidelines.

README.adoc

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+[[git-client-plugin]]
+= Git Client Plugin
+
+[[introduction]]
+== Introduction
+
+image:https://git-scm.com/images/logos/downloads/Git-Logo-2Color.png[Git logo,width=303,role=center,float=right]
+
+The git client plugin provides git application programming interfaces (APIs) for Jenkins plugins.
+It can fetch, checkout, branch, list, merge, and tag repositories.
+Refer to the https://javadoc.jenkins-ci.org/plugin/git-client/[API documentation] for specific API details.
+
+The https://javadoc.jenkins-ci.org/plugin/git-client/org/jenkinsci/plugins/gitclient/GitClient.html[GitClient interface] provides the primary entry points for git access.
+It supports username / password credentials and private key credentials using the https://plugins.jenkins.io/credentials[Jenkins credentials plugin].
+
+[[changelog]]
+== Changelog in https://github.com/jenkinsci/git-plugin/releases[GitHub Releases]
+
+Release notes are recorded in https://github.com/jenkinsci/git-client-plugin/releases[GitHub] beginning with git client plugin 2.8.1.
+Prior release notes are recorded in the git client plugin repository link:CHANGELOG.adoc#changelog-moved-to-github-releases[change log].
+
+[[implementations]]
+== Implementations
+
+The git client plugin default implementation requires that https://git-scm.com/downloads[command line git] is installed on the master and on every agent that will use git.
+Command line git implementations working with large files should also install https://git-lfs.github.com/[git LFS].
+The command line git implementation is the canonical implementation of the git interfaces provided by the git client plugin.
+
+Command line git is *enabled by default* when the git client plugin is installed.
+
+[[jgit]]
+=== JGit
+
+The git client plugin also includes two optional implementations that use https://www.eclipse.org/jgit/[Eclipse JGit].
+Eclipse JGit is a pure Java implementation of git.
+The JGit implementation in the git client plugin provides most of the functionality of the command line git implementation.
+When the JGit implementation is incomplete, the gap is noted in console logs.
+
+JGit is *disabled by default* when the git client plugin is installed.
+
+[[enabling-jgit]]
+=== Enabling JGit
+
+Click the "*Add Git*" button in the "*Global Tool Configuration*" section under "*Manage Jenkins*" to add JGit or JGit with Apache HTTP Client as a git implementation.
+
+image::images/enable-jgit.png[Enable JGit or JGit with Apache HTTP Client]
+
+=== JGit with Apache HTTP Client
+
+The original JGit implementation inside the git client plugin had issues with active directory authentication.
+A workaround was implemented to provide JGit but use Apache HTTP client for authentication.
+The issue in JGit has now been resolved and delivered in git client plugin releases.
+JGit with Apache HTTP Client continues to delivered to assure compatibility.
+
+== Windows Credentials Manager
+
+Git for Windows is able to integrate with the Windows Credentials Manager for secure storage of credentials.
+Windows Credentials Manager works very well for interactive users on the Windows desktop.
+Windows Credentials Manager does not work as well for batch processing in the git client plugin.
+It is best to disable Windows Credentials Manager when installing Git on Jenkins agents running Windows.
+
+== Bug Reports
+
+Report issues and enhancements with the https://issues.jenkins-ci.org[Jenkins issue tracker].
+
+== Contributing to the Plugin
+
+Refer to link:CONTRIBUTING.adoc#contributing-to-the-git-client-plugin[contributing to the plugin] for contribution guidelines.