What does this MR do?
GitLab 10.0 depends on the tracking database (because of the removal of System Hooks in !2644 (merged)), therefore the docs should clearly state how to set up and update the Geo tracking database.
To initiate synchronization it's no longer needed to push first. Geo will automatically pick up new projects, and it's no longer needed to push to the repo before GitLab Geo will start syncing.
Small changes to improve consistency through the whole docs.
What are the relevant issue numbers?
Closes gitlab-org/gitlab-ee#3365 and gitlab-org/gitlab-ee#3400