Merge "Add details about theme stability" into sc-dev am: 9aff8397 am: a35809b1 am: 4b52c680 am: 8960da3a

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/16176790

Change-Id: I2e8312ce8d4e83380704c67eac961c4030a26516