Rewrite runloop guide autorun FAQs

A rewrite of the autorun FAQs in the Runloop guide.

Fixes #1712 #1713 Partially addresses #1390
Nothing here is "within the autorun". If there is an autorun scheduled, I think it is a misnomer to say that you are "within" anything.

More accurate might be: "On this line, no autorun has been scheduled"

And on the schedule line, "Schedule creates an autorun to flush the runloop queues"

And on the scheduleOnce line "scheduleOnce adds an item to the queus of the scheduled autorun