Add a README that says to email me instead of using github mail.

What's with this new generation who hates email so much?

README

+
+Please read git-subtree.txt for documentation.
+
+Please don't contact me using github mail; it's slow, ugly, and worst of
+all, redundant. Email me instead at apenwarr@gmail.com and I'll be happy to
+help.
+
+Avery