Add SecurityError reasons for related origins

Author: MasterKale

index.bs

@@ -2285,6 +2285,9 @@ The following {{DOMException}} exceptions can be raised:
     :   {{SecurityError}}
     ::  The [=effective domain=] was not a [=valid domain=],
         or <code>{{PublicKeyCredentialCreationOptions/rp}}.{{PublicKeyCredentialRpEntity/id}}</code> was not equal to or a registrable domain suffix of the [=effective domain=].
+        In the case of [[#sctn-related-origins|related origin requests]],
+        the [=authenticator=] does not support it
+        or there were issues when [[#sctn-validating-relation-origin|validating related origins]].
 
     :   {{TimeoutError}}
     ::  The ceremony was cancelled by the user agent after exceeding the time limit permitted for the ceremony.
@@ -2848,6 +2851,9 @@ The following {{DOMException}} exceptions can be raised:
     :   {{SecurityError}}
     ::  The [=effective domain=] was not a [=valid domain=],
         or <code>{{PublicKeyCredentialCreationOptions/rp}}.{{PublicKeyCredentialRpEntity/id}}</code> was not equal to or a registrable domain suffix of the [=effective domain=].
+        In the case of [[#sctn-related-origins|related origin requests]],
+        the [=authenticator=] does not support it
+        or there were issues when [[#sctn-validating-relation-origin|validating related origins]].
 
     :   {{TimeoutError}}
     ::  The ceremony was cancelled by the user agent after exceeding the time limit permitted for the ceremony.