Update README

Modify to reflect recent changes and add description of introducing a
new target.

BUG=none
TEST=none

Change-Id: I7ddc217f3f7c1e41bce9dbcedce62507b30b2f72
Reviewed-on: https://gerrit-int.chromium.org/39564
Reviewed-by: Hung-Te Lin <hungte@google.com>
Commit-Queue: Vadim Bendebury <vbendeb@google.com>
Tested-by: Vadim Bendebury <vbendeb@google.com>
1 file changed