There isn't a GitHub Pages site here.

[BenVlodgi]

I was able find, what I assume is the same demo here:
http://airpair.github.io/demos/2014/09/T0021-airpair-angularjs-tutorial/#/

[keqiangliu]

In my case, my page repository uses the username/username.github.io naming scheme, but still cannot work.
I just clone the repository to local, and new a push_test.txt file and push it to the repository, and then https://username.github.io works.