I have a project together with several people and we have a README.md file with a bunch of GitHub Flavored Markdown that is rendered on our GitHub page. We also
Another method that I've gotten to work pretty successfully is using Ajax to fetch the docs using the Github API and a Javascript markdown engine to render the HTML (as also suggested by Nathan).
Nathan expressed some concern over performance but in my experience, it loads seemingly instantly so I don't think it's actually a problem.
The advantage is that it's easy to setup and it will always update your docs even if you just edit the markdown directly in a browser on github.
I set up an example on Github pages at http://bradrhodes.github.io/GithubDocSync/ to show it working.