I linked these docs form the help page pointing to a 404 and this takes care of adding some rather bare content so we have something up and running for a release.
These are important to help doc contributors get started. They have the side effect of pointing to a rather dangerous link for maintainers but any later changes should get blocked by the review policy later on.
I tried to only merge what makes sense for us, there is still quite some cleanup needed, this commit tries to preserve the 2.5 manual as much as possible while still keeping the rare new stuff from pro.
