ANDROID: Update README.md to document the automated external_updater workflow am: e2da333ce2 Original change: https://googleplex-android-review.googlesource.com/c/platform/external/ltp/+/40643964 Change-Id: I015b14bbce287c2cb97f9487600066d68850f9d1 Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>