Added downtime label to PROCESS.md
This does require some manual work (instead of an automatic solution as proposed in gitlab-org/gitlab-ce#14545), but it's an easy start and makes it very easy to see what merge requests require downtime.
This does require some manual work (instead of an automatic solution as proposed in gitlab-org/gitlab-ce#14545), but it's an easy start and makes it very easy to see what merge requests require downtime.