Address review comments

src/my-element.ts

@@ -1,3 +1,17 @@
+/**
+ * @license
+ * Copyright (c) 2019 The Polymer Project Authors. All rights reserved.
+ * This code may only be used under the BSD style license found at
+ * http://polymer.github.io/LICENSE.txt
+ * The complete set of authors may be found at
+ * http://polymer.github.io/AUTHORS.txt
+ * The complete set of contributors may be found at
+ * http://polymer.github.io/CONTRIBUTORS.txt
+ * Code distributed by Google as part of the polymer project is also
+ * subject to an additional IP rights grant found at
+ * http://polymer.github.io/PATENTS.txt
+ */
+
 import { LitElement, html, customElement, property, css } from 'lit-element';
 
 @customElement('my-element')