docs: Minor update to DP4 release notes
docs: Minor update to DP4 release notes

Added a new section from Dirk, with a couple of gotchas for people
updating from API level ≤22 to 24.

See first comment for doc stage location.

Change-Id: I237e9efac75b9c1e0fbeecf362dbc0de7c958c60

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base