Doc: fix description of privileges needed for ALTER PUBLICATION.

Adding a table to a publication requires ownership of the table
(in addition to ownership of the publication).  This was mentioned
nowhere.

doc/src/sgml/ref/alter_publication.sgml

@@ -62,11 +62,12 @@ ALTER PUBLICATION <replaceable class="parameter">name</replaceable> RENAME TO <r
 
   <para>
    You must own the publication to use <command>ALTER PUBLICATION</command>.
+   Adding a table to a publication additionally requires owning that table.
    To alter the owner, you must also be a direct or indirect member of the new
    owning role. The new owner must have <literal>CREATE</literal> privilege on
    the database.  Also, the new owner of a <literal>FOR ALL TABLES</literal>
    publication must be a superuser.  However, a superuser can change the
-   ownership of a publication while circumventing these restrictions.
+   ownership of a publication regardless of these restrictions.
   </para>
  </refsect1>