fix(keyboard): add link to plugin repo

Author: tlancina

js/utils/keyboard.js

@@ -23,7 +23,12 @@
  *   <div id="google-map"></div>
  * </div>
  * ```
- * 
+ * ----------
+ *
+ * ### Plugin Usage
+ * Information on using the plugin can be found at [https://github.com/driftyco/ionic-plugins-keyboard](https://github.com/driftyco/ionic-plugins-keyboard).
+ *
+ * ---------- 
  *
  * ### Android Notes
  * - If your app is running in fullscreen, i.e. you have `<preference name="Fullscreen" value="true" />` in your `config.xml` file