doc: improve readLine.pause()

The docs for readLine.pause are misleading. I seriously spent hours on this. If
it isn't a bug, at least it should be well documented.

Someone else stumbled on this too:
http://stackoverflow.com/questions/21341050/pausing-readline-in-node-js



Reviewed-by: Trevor Norris <trev.norris@gmail.com>
Reviewed-by: Chris Dickinson <christopher.s.dickinson@gmail.com>