Clarify that CREATEROLE roles are considered Administrators

Author: Michael Banck
Reviewed-By: Robert Treat
Discussion: https://postgr.es/m/2160a5071a7bb5339055b04a8cad81a822be9d8d.camel@credativ.de

doc/src/sgml/user-manag.sgml

@@ -492,10 +492,11 @@ DROP ROLE doomed_role;
 
   <para>
    <productname>PostgreSQL</productname> provides a set of default roles
-   which provide access to certain, commonly needed, privileged capabilities
-   and information.  Administrators can GRANT these roles to users and/or
-   other roles in their environment, providing those users with access to
-   the specified capabilities and information.
+   that provide access to certain, commonly needed, privileged capabilities
+   and information.  Administrators (including roles that have the
+   <literal>CREATEROLE</literal> privilege) can <command>GRANT</command> these
+   roles to users and/or other roles in their environment, providing those
+   users with access to the specified capabilities and information.
   </para>
 
   <para>