Add license to example file

Author: mosuem

pkgs/logging/example/main.dart

@@ -1,3 +1,7 @@
+// Copyright (c) 2024, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
 import 'package:logging/logging.dart';
 
 final log = Logger('ExampleLogger');