Better annotation comment indicating intended use

Doc/Sd1/objectsClasses.xml

@@ -13,8 +13,8 @@
     <title>Objects and classes</title>
 
     <annotation role="slide">
-      <para>Ignore me, just here to supply a valid annotation content
-      model.</para>
+      <para>This section and its children will appear as slides as
+      well.</para>
     </annotation>
 
     <para>Defining classes and creating objects.</para>