Initial docs

[abcoathup]

Initial docs based on READMEs and CLI and Lib docs.

Reference to import "@openzeppelin/upgrades/contracts/Initializable.sol"; will need to be updated once OpenZeppelin/openzeppelin-contracts#2335 merged and released.

network-files.adoc may need reworking.

---

Resolves #141

[frangio]

Looks good!

Can you delete the API docs from the readmes, and also the FAQ, so we avoid that duplication?

I've changed this PR to go into a new branch until we publish the docs site, so that content remains available by browsing the repo until then.

[abcoathup]

Can you delete the API docs from the readmes, and also the FAQ, so we avoid that duplication?

I removed API & FAQ.
Also removed How do the plugins work? (as this would have lots of links to docs FAQ) and Managing Ownership to avoid duplication.

[frangio]

We should also have links to the API docs, but it's okay if we don't do that in this PR.

[abcoathup]

@frangio what will the name of the docs URL be? Is it https://docs.openzeppelin.com/upgradesplugins or something else?

[frangio]

According to the current config the URL will be https://docs.openzeppelin.com/upgrades-plugins.

openzeppelin-upgrades/docs/antora.yml

Lines 1 to 3 in 8f142a4

	name: upgrades-plugins
	title: Upgrades
	version: 1.x

So the FAQ for example would be https://docs.openzeppelin.com/upgrades-plugins/faq. Note that this is an unversioned link that will get redirected to the latest version (https://docs.openzeppelin.com/upgrades-plugins/1.x/faq).

[frangio]

I changed the API links since they were pointing to the wrong page.

Thank you @abcoathup!