Once the transition is complete this should help to increase the quality and speed of development on Ruby. It is amazing how much contributions on projects go up, when moved to git/github.
The API docs are generated from comments in the code. To fix or add to the docs you need to get the source from svn, add your stuff, make a diff patch, and submit that patch to the ruby-doc or ruby-core mailing lists.
I've done it, its not that hard, but it's sort of tedious, and annoying enough that people who might otherwise want to help by adding a few notes or fixing the examples just won't.
Maybe I've just gotten used to it, but the use of git and github for this seems much simpler.