Clearify callback text in the tutorial

docs/tutorial.md

@@ -620,7 +620,7 @@ var CommentBox = React.createClass({
 });
 ```
 
-Let's call the callback from the `CommentForm` when the user submits the form:
+Now that `CommentBox` has made the callback available to `CommentForm` via the `onCommentSubmit` prop, the `CommentForm` can call the callback when the user submits the form:
 
 ```javascript{19}
 // tutorial19.js