We recently added a "Get started" link to Gitea, pointing to the
generic Developer's Guide. Now that the content is split between
"Getting started" and the reference "Developer's Guide", point
to Getting started content instead.
This should be a lot less intimidating for our new users.
Depends-On: https://review.opendev.org/715961
Change-Id: Ifa496bc8de1a6a39d7b52363db3ab49b8175ed9a