Mention ownership requirements for REFRESH MATERIALIZED VIEW in docs

Author: Dian Fay
Discussion: https://postgr.es/m/745abbd2-a1a0-ead8-2cb2-768c16747d97@gmail.com
Backpatch-through: 9.3

doc/src/sgml/ref/refresh_materialized_view.sgml

@@ -31,7 +31,8 @@ REFRESH MATERIALIZED VIEW [ CONCURRENTLY ] <replaceable class="parameter">name</
 
   <para>
    <command>REFRESH MATERIALIZED VIEW</command> completely replaces the
-   contents of a materialized view.  The old contents are discarded.  If
+   contents of a materialized view.  To execute this command you must be the
+   owner of the materialized view.  The old contents are discarded.  If
    <literal>WITH DATA</literal> is specified (or defaults) the backing query
    is executed to provide the new data, and the materialized view is left in a
    scannable state.  If <literal>WITH NO DATA</literal> is specified no new