In some minutes of searching yesterday afternoon on the docs site,
I couldn't find docs on how to set up our OAuth integrations for
the dev environment -- even though I was pretty sure they should
be there somewhere, because I'd just been told that. Wasn't until
I considered the problem fresh today, and grepped the docs source
instead, that I found them.
So, move them to a separate page so they're in the nav.
This better sets expectatations for the fact that in Zulip, the
Organization settings UI is available read-only to non-administrator
users.
Tweaked by tabbott to update some additional references.