Merge "[sf] Add readme for surfaceflinger frontend" into udc-dev am: 0f0d7b0309

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

Change-Id: If2f4731134461b7b5b75bee147b4b4f8f3055d10
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>