Merge "Add a high-level README.md" into sc-dev am: 30f0f9725c am: ca4001b5c2

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/modules/GeoTZ/+/14716254

Change-Id: I0047f35de474039d738ffc2b3500f985c2185f36