Merge "Add README.md for tools/compare_cts_reports/." into main am: 4b76dd3526

Original change: https://android-review.googlesource.com/c/platform/development/+/2758688

Change-Id: I1629e99b9e0e31cce0c089b9810b14a33a20a96f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>