fix docstring in events.js

example shows registering a handler, not triggering an event.

IPython/html/static/base/js/events.js

@@ -3,10 +3,11 @@
 
 // Give us an object to bind all events to. This object should be created
 // before all other objects so it exists when others register event handlers.
-// To trigger an event handler:
+// To register an event handler:
+//
 // require(['base/js/events'], function (events) {
-//     events.on("event.Namespace", function () {do_stuff(); });
-// })
+//     events.on("event.Namespace", function () { do_stuff(); });
+// });
 
 define(['base/js/namespace', 'jquery'], function(IPython, $) {
     "use strict";