update_engine: update help text am: 96eb042527

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2959226

Change-Id: I51ab59ddcba44a9c1404b72dbd8ae3c6a3d4d967
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>