doc/README: add note regarding virtual subclassing

README.md

@@ -85,6 +85,8 @@ Where Qt returns a C++ object by value (e.g. `QSize`), the binding may have move
 
 The `connect(sourceObject, sourceSignal, targetObject, targetSlot)` is projected as `targetObject.onSourceSignal(func()...)`.
 
+- You can also override virtual methods like PaintEvent in the same way. Your callback `func()` receives `super()` as a first argument that can be used to call the base class implementation.
+
 Qt class inherited types are projected as a Go embedded struct. For example, to pass a `var myLabel *qt.QLabel` to a function taking only the `*qt.QWidget` base class, write `myLabel.QWidget`.
 
 - When a Qt subclass adds a method overload (e.g. `QMenu::addAction(QString)` vs `QWidget::addAction(QAction*)`), the base class version is shadowed and can only be called via `myQMenu.QWidget.AddAction(QAction*)`.