cf. thread

• We currently claim that you can bring MachinePools along when you adopt a cluster, but our documentation doesn't tell you how. Figure out if this is possible: if so, document how; if not, correct the documentation.
• Is it possible to adopt existing msets for an already-managed cluster by creating one or more MachinePools? (If it is possible to adopt with the cluster as implied above, it would seem like it should Just Work™, but...) If not, let's document that, and create a card to add support for it (linked to HIVE-2043, the "unadopt" side). If so, let's document how. If it is possible, but awkward (e.g. you have to pause controllers, disable webhooks, add labels to the spoke msets, etc.) then let's card making it smoother.