[automerger skipped] [DataStore] Add README.md am: c3829761 -s ours

am skip reason: Merged-In I1f88bf56361536b5e4fdec501f51de4639636556 with SHA-1 bcb4a3a9 is already in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/26560933



Change-Id: I94d54445077dc9d93d5461d6f89f530da03a12d6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>