gh-pages-no-jekyll
What about a Wiki?
As an alternative, consider using the Wiki feature on GitHub.
It will give a similar Github-styled experience of doc pages that separate from the code and files, but with the benefit of a menu. Note that a Wiki lives in its own repo, so updates made independently to the main part of the repo. A Wiki has a history, but does it not work Pull Requests and reviews so the edit process is different.