[automerger skipped] Add documentation about ART Service. am: bb7c41c476 am: 1d21821b1f am: 26eb11ec71 -s ours

am skip reason: Merged-In Ia8ab6703b906d3c5232dc6c4acea458de84d2f9c with SHA-1 e231149f38 is already in history

Original change: https://android-review.googlesource.com/c/platform/art/+/2612930

Change-Id: I3aaef56d2e2c5df17a04a7b7742d050dd7acee52
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>