Update draft-davidben-tls-merkle-tree-certs.md

Co-authored-by: David Benjamin <davidben@davidben.net>

Author: cjpatton

draft-davidben-tls-merkle-tree-certs.md

@@ -647,7 +647,7 @@ The attribute's value is a RELATIVE-OID containing the trust anchor ID's ASN.1 r
 
 For initial experimentation, early implementations of this design will:
 
-1. Use UTF88String to represent the attribute's value rather than RELATIVE-OID.
+1. Use UTF8String to represent the attribute's value rather than RELATIVE-OID. The UTF8String contains trust anchor ID's ASCII representation, e.g. `324731.1`.
 
 1. Use the OID 1.3.6.1.4.1.44363.47.1 instead of `id-rdna-trustAnchorID`.