ensure all topic overviews have an horizontal rule with the list of the sections above

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52257 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/doxygen/overviews/app.h

@@ -12,13 +12,15 @@
 
  Classes: wxApp
 
-
+ @li @ref overview_app_intro
  @li @ref overview_app_shutdown
 
 
  <hr>
 
 
+ @section overview_app_intro Introduction
+
  A wxWidgets application does not have a @e main procedure; the equivalent is the
  wxApp::OnInit member defined for a class derived from wxApp.