Supplying slide exclude hint

Doc/Templates/docbookSnippets.xml

@@ -52,6 +52,12 @@ http://xahlee.info/comp/unicode_drawing_shapes.html <co xml:id="dummy"/>
           <para/>
         </callout>
       </calloutlist>
+
+      <note>
+        <para>The preceding <tag class="starttag">calloutlist role =
+        "slideExclude"</tag> excludes the whole block from appearing in
+        slides.</para>
+      </note>
     </figure>
   </section>