Clarify use of arrow functions

Per 1db20999f0 (commitcomment-12865588).

docs/08.1-more-about-refs.md

@@ -90,7 +90,7 @@ It's as simple as:
 
 The `ref` attribute can be a callback function instead of a name.  This callback will be executed immediately after the component is mounted.  The referenced component will be passed in as a parameter, and the callback function may use the component immediately, or save the reference for future use (or both).
 
-It's as simple as assigning a `ref` attribute to anything returned from `render` such as:
+It's as simple as adding a `ref` attribute to anything returned from `render` by using an ES6 arrow function:
 
 ```html
   render: function() {