Write QProperty use in QML

Details: Added a note on how QProperty works in QML using BINDABLE keyword

Task-number: QTBUG-89166
Change-Id: Ib48dd26b0724f906efa65d14fbb75a8b97255b05
Reviewed-by: Fabian Kosmale <[email protected]>

src/corelib/kernel/qproperty.cpp

@@ -1175,6 +1175,17 @@ QString QPropertyBindingError::description() const
   dynamically, the binding expression. It is represented as a C++ lambda and
   can be used to express relationships between different properties in your
   application.
+
+  \note In the case of QML it is important that \l QProperty needs to be exposed
+  in \l Q_PROPERTY with the BINDABLE keyword. As a result the QML engine, uses it
+  as the bindable interface to set up the property binding. In turn, the binding
+  can be then interacted with C++ via the normal API like:
+
+  QProperty<T>::onValueChanged, QProperty::takeBinding and QBindable::hasBinding
+
+  If the property is BINDABLE, then the engine will use the change-tracking
+  inherent to the C++ property system for getting notified about changes; and
+  won't rely on signals being emitted.
 */
 
 /*!