fix(backup): parameter name

close eXist-db#1033

Author: duncdrum

src/main/xar-resources/data/backup/backup.xml

@@ -537,7 +537,7 @@
             <programlisting xlink:href="listings/listing-10.txt"/>
             <para>The restore process compares app packages contained in the backup with those already installed in the database. By default, older versions of
                 an application package contained in the backup will not be restored if a newer version is installed in the database. To change this behavior and
-                enforce an overwrite, pass parameter <literal>--overwrite</literal>.</para>
+                enforce an overwrite, pass parameter <literal>--overwrite-apps</literal> or <literal>-a</literal>.</para>
         </sect2>
 
         <sect2 xml:id="repair">