Talk about the "instance atom" instead of "an instance" to minimize heart attacks.  Suggest a course of action too.


Don't talk about Python 3 at all.  That can come later, or hopefully may even
have been deleted by that point.

refs #7653


git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/branches/deprecate-jelly-instance-support-7653@43245 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb