Removes the notice regarding branch name changes from the main
README file. Also changes the default branch to 'master' in the
.gitreview file.
Change-Id: I77f7115751a2b469f13dd51c159ec7d3f2fc1a12
Additionally aligned between Treasuremap and Airshipctl to use the same
environment variable name "SITE" for a site name.
Change-Id: Id6405b7074d34bc73d730eea76d9dd6ab7901405
Signed-off-by: James Gu <james.gu@att.com>