GitLab

The page had gotten badly out of date. This CL rewrites most
of it to reflect current policy and practice and stops pointing
to viewvc for other links ;)

Change-Id: I62cc952a6f56954af723f4d57b2fadfd84227bda
Reviewed-on: https://chromium-review.googlesource.com/c/1298650
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Chris Palmer <palmer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604750}