add comment for idle time

Author: xinyzhou

dotnet/InkRecognition/wpf-app/src/MainWindow.xaml.cs

@@ -19,6 +19,7 @@ public partial class MainWindow : Window
         InkRecognizer inkRecognizer;
         DisplayInformation displayInfo;
         private readonly DispatcherTimer dispatcherTimer;
+        // Time to wait before triggering ink recognition operation
         const double IDLE_WAITING_TIME = 1000;
 
         public MainWindow()