Documentation has been a problem for a while.
Looking through the unit tests for Rhino.Mocks on Github helps but only from a simplistic standpoint. As Patrick has pointed out, Stackoverflow is a good resource but those have a tendency to be for a specific case or issue.
Ayende use to have a few pages out there that covered the basics but have since then been pulled.
The current thought is to simply utilize Github's wiki capabilities to cover the basic "how to's."
Feel free to post any questions that you might have.