Added some documentation for Linux modal dialog fix

Author: githubuser0xFFFF

src/FloatingDockContainer.cpp

@@ -516,6 +516,8 @@ void FloatingDockContainerPrivate::updateDropOverlays(const QPoint &GlobalPos)
 	}
 
 #ifdef Q_OS_LINUX
+	// Prevent display of drop overlays and docking as long as a model dialog
+	// is active
     if (qApp->activeModalWidget())
     {
         return;