Make OSXIsGUIApplication() documentation more clear for non Mac people.

Provide a more detailed explanation of what this function does and does not.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75204 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/app.h

@@ -881,9 +881,19 @@ public:
     virtual void MacReopenApp();
 
     /**
-        Called during startup, if a non-bundled application wants to
-        stay in background, then it has to override this to return false
-        otherwise the app will be brought to the foreground.
+        May be overridden to indicate that the application is not a foreground
+        GUI application under OS X.
+
+        This method is called during the application startup and returns @true
+        by default. In this case, wxWidgets ensures that the application is ran
+        as a foreground, GUI application so that the user can interact with it
+        normally, even if it is not bundled. If this is undesired, i.e. if the
+        application doesn't need to be brought to the foreground, this method
+        can be overridden to return @false.
+
+        Notice that overriding it doesn't make any difference for the bundled
+        applications which are always foreground unless @c LSBackgroundOnly key
+        is specified in the @c Info.plist file.
 
         @onlyfor{wxosx}