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
Updates the main README file with a notice regarding upcoming
changes to the branching structure.
Relates-To: #50
Change-Id: I9098d07338cfd069aec255933b5bb95542f5595e