Train & document how to perform failovers using repmgr

Repmgr was recently introduced so we now finally have a working failover system. However I personally don't really know how it works and I can imagine others having the same problems. We need to ensure there's proper documentation (this may already be the case) and that all database specialists are familiar with the procedures. Further we need to ensure that the onboarding process includes training on how to perform failovers and the likes.