document arcane NOTICE display behaviour

[DanielOaks]

I think clients that receive a NOTICE generally display it in the server buffer if a query window doesn't already exist. e.g. if you just message ChanServ that's what'll happen on mirc, etc. I should note this down, because it's somewhat related to #6 and the dot-in-nick-equals-servername heuristic stuff that seems to be somewhat common (tbh I'm pretty sure that modern right now even describes that as being a solid rule, probably something to change in there as well, etc).