Document some runbook steps for #426
There was some investigation done in #426 (closed). It would be nice to write down a few commands that might be useful to reuse when we run into a similar issue again.
In !22 (merged), I've started the runbooks as a boilerplate. They are not holy, and only should help us retrieving useful information. It's no problem if anything is missing from the runbook, we just try to keep iterating on them.