[docs] Make sure JSX comments code is in block

docs/02.1-jsx-in-depth.md

@@ -152,6 +152,7 @@ var content = Container(null, window.isLoggedIn ? Nav(null) : Login(null));
 ### Comments
 
 It's easy to add comments within your JSX; they're just JS expressions:
+
 ```javascript
 var content = <Container>{/* this is a comment */}<Nav /></Container>;
 ```