Added note about NotifyTaskCompletion<T>

Author: Sergio0694

docs/mvvm/ObservableObject.md

@@ -84,6 +84,9 @@ public class MyModel : ObservableObject
 
 Here the `SetPropertyAndNotifyOnCompletion<TTask>(ref TTask, Expression<Func<TTask>>, TTask, string)` method will take care of updating the target field, monitoring the new task, if present, and raising the notification event when that task completes. This way, it's possible to just bind to a task property and to be notified when its status changes.
 
+> [!NOTE]
+> The `SetPropertyAndNotifyOnCompletion` method is meant to replace the usage of the `NotifyTaskCompletion<T>` type from the `Microsoft.Toolkit` package. If this type was being used, it can be replaced with just the inner `Task` (or `Task<TResult>`) property, and then the `SetPropertyAndNotifyOnCompletion` method can be used to set its value and raise notification changes. All the properties exposed by the `NotifyTaskCompletion<T>` type are available directly on `Task` instances.
+
 ## Sample Code
 
 There are more examples in the [unit tests](https://github.com/Microsoft/WindowsCommunityToolkit//blob/master/UnitTests/UnitTests.Shared/Mvvm).