Move the README file to markdown so that it makes the github page look
prettier. I know that github repo is a mirror and not the official
repo, but I think it doesn't hurt to have it in markdown format.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Message-Id: <20160715043111.29007-1-bobby.prani@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>