Adding links to the merge requests and group documentation.

Created by: thomasbiddle

Almost didn't realize there was an api for merge requests - Was about to add support for it when I saw it, so just needed to add links to the documentation :-)

As a heads up - I didn't run this on my local (Running into some issue with the haml parsing - Just errors out - Does that before my change as well though). If someone would be so kind as to run this on their local to test, then it should be good to go.