added documentation with an image

source/RobotAPI/gui_plugins/PlatformUnitPlugin/PlatformUnitGuiPlugin.h

@@ -69,6 +69,11 @@ namespace armarx
       \ingroup ArmarXGuiPlugins
 
       \see PlatformUnitGuiPlugin
+
+      \image html PlatformUnitGuiPlugin_widgetpng.png "The plugin's ui." width=300px
+            -# The current position and rotation, fields to enter a new target and a button to set the platform in motion.
+            -# A joystick like control widget to move the platform. It has two speed level. The platform does not rotate to move in a direction. Up moves the platform forward.
+            -# A joystick like control widget to rotate the platform.
       */
     class PlatformUnitWidget :
             public ArmarXComponentWidgetController,