Root README.md file.

Bug: 
Change-Id: I5d4f5fedeab490a8d254b550650f56be9777918c
Reviewed-on: https://chromium-review.googlesource.com/592454
Commit-Queue: Vincent Scheib <scheib@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490550}
2 files changed