Merge pull request reactjs#433 from sznowicki/patch-1

Update `React.PureComponent` reference.

Author: bvaughn

content/docs/reference-react.md

@@ -71,7 +71,7 @@ See the [React.Component API Reference](/docs/react-component.html) for a list o
 
 ### `React.PureComponent`
 
-`React.PureComponent` is exactly like [`React.Component`](#reactcomponent), but implements [`shouldComponentUpdate()`](/docs/react-component.html#shouldcomponentupdate) with a shallow prop and state comparison.
+`React.PureComponent` is similar to [`React.Component`](#reactcomponent). The difference between them is that [`React.Component`](#reactcomponent) doesn't implement [`shouldComponentUpdate()`](/docs/react-component.html#shouldcomponentupdate), but `React.PureComponent` implements it with a shallow prop and state comparison. 
 
 If your React component's `render()` function renders the same result given the same props and state, you can use `React.PureComponent` for a performance boost in some cases.