Merge "Document the allowed challenge size" into main am: 4f73689e26

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/2813217

Change-Id: Ifd5b1ef1e80649d43119fe0f8edd5cb51efaebaf
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>