Add .NET progress notification example

Author: dacharyc

source/includes/api-details/csharp/sync/manage-sync-sessions-check-upload-and-download-progress-description.rst

@@ -24,3 +24,7 @@ as a double between 0.0 and 1.0.
 
 Once you no longer wish to receive notifications, unregister the token with 
 ``token.Dispose()``.
+
+In the following example, we subscribe to a progress observable on the
+``session`` to listen for upload events. When this callback is triggered, it
+prints the upload progress as a percentage.

source/includes/sdk-examples/sync/manage-sync-sessions-check-upload-download-progress.rst

@@ -10,7 +10,7 @@
      - id: csharp
        content: |
 
-         .. literalinclude:: /examples/MissingPlaceholders/example.cs
+         .. literalinclude:: /examples/generated/dotnet/ProgressNotifications.snippet.upload-download-progress-notification.cs
             :language: csharp
 
      - id: dart