Doc'd that extra_email_context can be used to override default template context values in PasswordResetView.

docs/topics/auth/default.txt

@@ -1292,7 +1292,8 @@ implementation details see :ref:`using-the-views`.
       link. By default, HTML email is not sent.
 
     * ``extra_email_context``: A dictionary of context data that will be
-      available in the email template.
+      available in the email template. It can be used to override default
+      template context values listed below e.g. ``domain``.
 
     **Template context:**