Add README am: 3aeba4cab6 am: 591bf2432c am: f9cd093ca0 am: ec2af4c798

Original change: https://android-review.googlesource.com/c/platform/packages/apps/Messaging/+/2614297

Change-Id: I658ce911ace74ab76f67954cb220289b4cd2f515
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>