Document how to make dashboards

Related to checking out performance metrics #1830 (closed)

what is the connection between the grafana repo at https://gitlab.com/gitlab-org/grafana-dashboards/tree/master/dashboards and the dashboards in grafana? Does MR to repo create the dashboard? Not documented?

Discussed with @stanhu and found

• repo looks obsolete, and no, submitting an MR to the repo does not generate the dashboard.
• repo seems to have a script to scrape dashboards from grafana; this hasn't been run in a while.
• what is purpose of repo? perhaps to have a quick way to back up dashboard json files in case performance.gitlab.net goes byebye?
• to make a new dashboard:
  • log in to performance.gitlab.net, click on Home, option appears to make dashboard if you are admin.
  • Admins can make other people admins. Not documented who admins are or who should be? Any objections to making developers admins as well? Or at least all team leads?
  • When creating a dashboard, multiple "data sources" present themselves. These should also be explained in documentation.

@yorickpeterse @pcarranza I'm happy to make the MR, but can you help answer some of the questions here and perhaps point out that it is documented (in which case: great, where?)