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

Merge "[sf] Add readme for surfaceflinger frontend" into udc-dev am: 0f0d7b03 am: 7a66ef37 am: 1a6b6fca

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



Change-Id: I50675ad66280255b9be9e2f1fd5506f47102cae1
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>