Add README
Add README

Add a basic README file which explains the basics of what we have and
how to use it.

Signed-off-by: Brendan Higgins <814c78e64718876fcf28699d7bb509bf090f2495@google.com>
Change-Id: I34d5feae74f67505b8ceeb4f036efff81774818e

google/lkml-gerrit-bridge