Added "Documenting Python" to the index.

Doc/html/index.html

@@ -28,6 +28,9 @@
 
       <LI> <A HREF="api/api.html">Python/C API</A>
 	(reference for C/C++ programmers)
+
+      <LI> <A HREF="doc/doc.html">Documenting Python</A>
+	(information for documentation authors)
     </UL>
 
   </BODY>