Add an example on the demo page

Author: steffen

examples/index.html

@@ -46,7 +46,9 @@
 
   <img src="https://github.com/hubot.png" width="100" alt="hubot">
 
-  <textarea cols="50" rows="10"></textarea>
+  <p>Test by copying this page's URL and then selecting <i>here</i> in the textarea and pasting the URL.</p>
+
+  <textarea cols="50" rows="10">The examples can be found here.</textarea>
 
   <script type="module">
     // import subscribe from '../dist/index.esm.js'