Add README am: 3aeba4cab6 am: 591bf2432c

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

Change-Id: I6fa9f9f108e9af79cadd6679b1e2c12d0cb6df19
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>