Ensure that README file makes it into the tarball

setup.cfg depends on the README file for its long description, so if
it's not in the source tarball, the build will bomb out. README.rst is an
automatically grokked name of a file for python and gets included
automatically. While we're dealing with this, add a MANIFEST.in to
ensure that AUTHORS and ChangeLog get installed too.

Change-Id: Id59fa5a6fecc179a80710ba8a5dc898fb713b1cf