Rewrite runloop guide autorun FAQs

A rewrite of the autorun FAQs in the Runloop guide.

Fixes #1712 #1713 Partially addresses #1390
This is very mis-leading. `before Ember finds out about the click` <- I'm unsure what this is referring to.

When you schedule or scheduleOnce, an autorun (if not already scheduled) is scheduled the flush the queues. It is akin to `setTimeout(function(){ Ember.run.end(); }, 0);`.

Nothing is "found out".