I actually used a similar technique for a course I taught on rapid web prototyping, it turned out well: https://github.com/amontalenti/rapid-web/tags
The other cool thing about setting up these tags is making it easy to use Github's compare view to see the differences between any number of steps. e.g. in his example, here is the difference between step 0 and step 1 of his tutorial:
https://github.com/emmett9001/iPhoneGameDemo/compare/0_ready...