Adding some info about event callbacks

docs/docs/reference/_binders/on-[event].md

@@ -5,3 +5,40 @@ Binds an event listener on the element using the event specified in `[event]` an
 ```html
 <button rv-on-click="item.destroy">Remove</button>
 ```
+
+*The callback function is passed 1: an event object and 2: the bound context which will also include named references to nested bindings.*
+
+```html
+<ul>
+  <li rv-each-a="view.a">
+    <ul>
+      <li rv-each-b="a.b">
+        <button rv-on-click="view.clicked">third</button>
+      <li>
+    </ul>
+  <li>
+</ul>
+```
+
+```javascript
+view = {
+	a: [ { b:[ { "..." } ] } ],
+	clicked: function(e, bound){
+		console.log(bound);
+	}
+}
+
+rivets.bind(el, {view: view});
+```
+
+```
+//console output:
+{
+	view: {...}, 
+	b: {...}, 
+	a: {...}, 
+	index:n
+}
+```
+
+*Also note that the arguments passed to the event callback can be [reconfigured](/docs/guide/#usage-configuring) through the `handler` property.*