Merge "Add some warnings and notes about framework's jarjar rules" into sc-dev...

Merge "Add some warnings and notes about framework's jarjar rules" into sc-dev am: c8863205 am: a19d2748 am: 22a4cd5c

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/14703099

Change-Id: I5763ad3a611fbd2dbddf581514abd81ec52ccaf5