Update tutorial with reference to autobinding docs (#6870)

* Update tutorial with reference to autobinding docs

* Update tutorial to clarify that autobinding happens specifically with createClass() API

docs/tutorial.md

@@ -524,6 +524,8 @@ var CommentForm = React.createClass({
 
 React attaches event handlers to components using a camelCase naming convention. We attach `onChange` handlers to the two `<input>` elements. Now, as the user enters text into the `<input>` fields, the attached `onChange` callbacks are fired and the `state` of the component is modified. Subsequently, the rendered value of the `input` element will be updated to reflect the current component `state`.
 
+(The astute reader may be surprised that these event handlers work as described, given that the method references are not explicitly bound to `this`. `React.createClass(...)` [automatically binds](/react/docs/interactivity-and-dynamic-uis.html#under-the-hood-autobinding-and-event-delegation) each method to its component instance, obviating the need for explicit binding.)
+
 #### Submitting the form
 
 Let's make the form interactive. When the user submits the form, we should clear it, submit a request to the server, and refresh the list of comments. To start, let's listen for the form's submit event and clear it.