Added small example of attaching event listeners

This closes https://github.com/select2/select2/pull/4255

docs/_includes/options/events/jquery.html

@@ -50,6 +50,12 @@
     How can I attach listeners for these events?
   </h3>
 
+{% highlight js linenos %}
+$('select').on('select2:select', function (evt) {
+  // Do something
+});
+{% endhighlight %}
+
   {% include options/not-written.html %}
 
   <h3>