@quirkey has written a great Guide to GitHub Pages, specifically on using the built-in Jekyll integration.

img http://img.skitch.com/20090504-n4wr7imm2bk9de3w234c9qg167.png http://www.quirkey.com/blog/2009/05/01/github-pages-for-fun-and-win

Check it out and start busting out some awesome documentation for your projects!