Clarify that multisig control to change is DID Method specific.

Co-authored-by: Ted Thibodeau Jr 

Author: msporny

index.html

@@ -4030,7 +4030,7 @@ Group Control
 Section [[[#verification-methods]]] or can be an intrinsic part of the
 verification material of the [=verification method=], where the number of [=DID controllers=] that
 participated in the generation of a particular digital signature are hidden for
-privacy reasons.
+privacy reasons. Verification methods that require a proof be produced by a combination of cryptographic operations performed by members of a group can be used to control the contents of a DID document; exactly how this is realized depends on individual DID method specifications.
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 From a functional standpoint, this option is