more clarity on where to get gitlab.com support
Fixes https://gitlab.com/gitlab-com/peopleops/issues/65
The info was already on the page, but it was a bit hidden. Since GitLab.com is a prominent aspect of GitLab, it makes sense to elevate the visibility here a bit.
Also did some boy scouting by adding a TOC (I felt the page had become very much a wall of text, and in fact it can still use more structure), and by making sure that "References" is the last section.
\cc @balameb