Identity Credential: Update docs to mention valid range for ACP identifiers.

Bug: 155100967
Test: atest android.security.identity.cts
Merged-In: I850e667676d3488be786447ed3ad33c80444f5e2
Change-Id: I95b909d3e87a1377c3ee5f264d3e519183c51bec
2 files changed