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

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



Change-Id: I839500353627df00296cbf556965407d066d2033
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>