plugins/org.eclipse.gendoc.doc.pptx/plugin.xml

<?xml version="1.0" encoding="UTF-8"?>
<?eclipse version="3.4"?>
<plugin>

   <extension
         point="org.eclipse.help.toc">
      <toc
            file="pptx_userguide.xml">
      </toc>
   </extension>

</plugin>