Document what JWT Audience does, and what could happen if you change it

[tim-elmer]

Not sure I'd call this a bug.

I'll admit, changing something I didn't fully understand was probably a bad idea. In my defense, the help text says "Usually your domain name. (e.g. urn:your.domain.com)". Well, I just spent the last half-hour figuring out how to edit JSON in PSQL to undo that change.

As stated in the title, it would probably be a good idea to warn users that they can render their instance inaccessible by changing the JWT audience incorrectly.