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

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

Change-Id: I8232106a31e1d06b281a4d58d10ab82422c54a9b