Amended contribution guidelines

Copied widely accepted guidelines from
https://github.com/sindresorhus/awesome-nodejs.

Dropped the strictest requirements, ending up with a list of
reasonable guidelines, while still being awesome compliant.

Part of #9.

CONTRIBUTING.md

@@ -2,5 +2,30 @@
 
 We welcome contributions to this list of high-quality Move content--just send a pull request!
 
-As the list grow over time, we may do more curation by splitting some sections from the list into separate docs and highlight a smaller set of prominent projects on the front page.
+As the list grows over time, we may do more curation by splitting some sections from the list into separate docs and highlight a smaller set of prominent projects on the front page.
+
 However, we will always bias toward inclusion of anything a Move community member might find interesting or useful.
+
+## PR requirements
+Ensure your addition and the pull request adheres to the following guidelines:
+
+- **Use the following format**: `[project](link) - Description.`
+- If you submit a project that is similar to an existing project in the list, argue how it's better.
+- Search previous suggestions before making a new one, as yours may be a duplicate.
+- Make an individual pull request for each suggestion.
+- Additions should be added to the bottom of the relevant category.
+- Link to the GitHub repo, if applicable.
+- Keep descriptions short and simple, but descriptive.
+- Descriptions should not be marketing taglines.
+- Descriptions should not be title-case.
+- Start the description with a capital and end with a full stop/period.
+- Check your spelling and grammar.
+- No trailing whitespaces.
+- The pull request should have a useful title and include a link to the package and why it should be included.
+- New categories or improvements to the existing categorization are welcome, but should be done in a separate pull request. **Remember to update the [`Contents`](README.md#contents)!**
+
+Thank you for your suggestion!
+
+## Updating your PR
+
+A lot of times, making a PR adhere to the standards above can be difficult. If the maintainers notice anything that we'd like changed, we'll ask you to edit your PR before we merge it. If you're not sure how to do that, [here is a guide](https://github.com/RichardLitt/knowledge/blob/master/github/amending-a-commit-guide.md) on the different ways you can update your PR so that we can merge it.