Merge "[sf] Add readme for surfaceflinger frontend" into udc-dev am:...

Merge "[sf] Add readme for surfaceflinger frontend" into udc-dev am: 0f0d7b03 am: 41fb2c90 am: 3b13bff3 am: 18a524cb

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/native/+/23272393



Change-Id: Ib46d93bebcade3757832e96f91a5d396c4366938
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>