Update conditional-rendering.md (#8636)

Stating the fact that component lifecycle methods will still fire as normal even though you return null from the render method.

docs/conditional-rendering.md

@@ -238,3 +238,5 @@ ReactDOM.render(
 ```
 
 [Try it on CodePen.](https://codepen.io/gaearon/pen/Xjoqwm?editors=0010)
+
+Returning `null` from a component's `render` method does not affect the firing of the component's lifecycle methods. For instance, `componentWillUpdate` and `componentDidUpdate` will still be called.