Document wxBitmapToggleButton XRC parameters.

Describe the properties specific to this class in the XRC format
documentation.

Closes #13204.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67717 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/doxygen/overviews/xrc_format.h

@@ -586,6 +586,17 @@ Example:
 @endcode
 
 
+@subsubsection xrc_wxtogglebuttton wxBitmapToggleButton
+
+@beginTable
+@hdr3col{property, type, description}
+@row3col{bitmap, @ref overview_xrcformat_type_bitmap,
+     Label to display on the button (required).}
+@row3col{checked, @ref overview_xrcformat_type_bool,
+     Should the button be checked/pressed initially (default: 0)?}
+@endTable
+
+
 @subsubsection xrc_wxbutton wxButton
 
 @beginTable