You can clone the Github repo and then run a local webserver to access it at localhost:8000/book.html (there is a `make.sh` build script, but the repo already contains the produced HTML).

You can also fork the repo, enable Github Pages, and then access it at yourgithubname.github.io/python-opengl/book.html

I just made a Github issue suggesting to the author, if he's not opposed to using Github pages himself: https://github.com/rougier/python-opengl/issues/38