Just a quick guide on methods I've seen to document GitHub projects. This is not a complete list by any means, just things I've ran across and bookmarked.
- GitHub Wiki's
- GitHub Sites
- A directory of markdown or AsciiDoc files
- Sphinx generated documentation
- Publish your documents to Read the Docs so they are searchable, etc. I'd imagine this works well with Sphinx generated docs.
- Document REST API's with Swagger
- Keep a personal wiki using Gollum (the GitHub wiki engine) instead of something like Evernote