Explore alternatives to readthedocs for documentation.

[kiran-kate]

Readthedocs has following issues:

1. It has advertisements on the bottom left pane.
2. The build fails randomly and we don't get notified. Sometimes, only a few pages render with issues and we don't discover it unless we happen to open those pages.

Would be helpful to find an alternative if possible. Github pages is one option, not sure of others.

[shinnar]

#1268 should address (2)