Ci docs

[j0yu]

Testing out tk-doc-generator

See https://developer.shotgunsoftware.com/tk-doc-generator/53726823/?title=Integrating+the+Doc+Generator

Ran into a limitation where trying to include sphinx built API docs within the just-the-docs doctree required a lot more work that's beyond the scope of this PR and these tk-doc-generator PRs:

• https://github.com/shotgunsoftware/just-the-docs/pull/10
• https://github.com/shotgunsoftware/tk-doc-generator/pull/24
• https://github.com/shotgunsoftware/tk-doc-generator/pull/22
• https://github.com/shotgunsoftware/just-the-docs/pull/9
• https://github.com/shotgunsoftware/tk-doc-generator/pull/21

Using normal Sphinx RST workflow instead, deprecated GitHub Wiki. Hosting docs on GitHub Pages