Add preferred_username to app.example.ini

Author: SimonErm

custom/conf/app.example.ini

@@ -1553,8 +1553,9 @@ LEVEL = Info
 ;; The source of the username for new oauth2 accounts:
 ;; userid = use the userid / sub attribute
 ;; nickname = use the nickname attribute
+;; preferred_username = use the preferred_username attribute
 ;; email = use the username part of the email attribute
-;; Note: `nickname` and `email` options will normalize input strings using the following criteria:
+;; Note: `nickname`, `preferred_username` and `email` options will normalize input strings using the following criteria:
 ;; - diacritics are removed
 ;; - the characters in the set `['´\x60]` are removed
 ;; - the characters in the set `[\s~+]` are replaced with `-`