Add a comment to tooltip window to clarify it's use in plug-ins

modules/juce_gui_basics/windows/juce_TooltipWindow.h

@@ -32,14 +32,17 @@
 
     To enable tooltips in your app, just create a single instance of a TooltipWindow
     object. Note that if you instantiate more than one instance of this class, you'll
-    end up with multiple tooltips being shown!
+    end up with multiple tooltips being shown! This is a common problem when compiling
+    audio plug-ins with JUCE: depending on the way you instantiate TooltipWindow,
+    you may end up with a TooltipWindow for each plug-in instance. To avoid this use a
+    SharedResourcePointer to instantiate the TooltipWindow only once.
 
     The TooltipWindow object will then stay invisible, waiting until the mouse
     hovers for the specified length of time - it will then see if it's currently
     over a component which implements the TooltipClient interface, and if so,
     it will make itself visible to show the tooltip in the appropriate place.
 
-    @see TooltipClient, SettableTooltipClient
+    @see TooltipClient, SettableTooltipClient, SharedResourcePointer
 */
 class JUCE_API  TooltipWindow  : public Component,
                                  private Timer