Clarify that given_name and name are not to be composed (#731)

* Clarify that given_name and name are not to be composed

* link

Author: npm1

spec/index.bs

@@ -2046,7 +2046,11 @@ Every {{IdentityProviderAccount}} is expected to have members with the following
     :   <dfn>username</dfn>
     ::  The user's username.
     :   <dfn>given_name</dfn>
-    ::  The user's given name.
+    ::  The user's given name. Note that {{IdentityProviderAccount/given_name}} and
+        {{IdentityProviderAccount/name}} are separate fields. Whereas
+        {{IdentityProviderAccount/name}} is a full name, {{IdentityProviderAccount/given_name}} may
+        be a nickname. In particular, this means that these two fields should not be composed
+        together.
     :   <dfn>picture</dfn>
     ::  URL for the account's picture.
     :   <dfn>approved_clients</dfn>