fix spelling error

Author: Chris Wheatley

README.md

@@ -106,7 +106,7 @@ var User = React.createClass({
 });
 
 // Declarative route configuration (could also load this config lazily
-// instead, all you reall need is a single root route, you don't need to
+// instead, all you really need is a single root route, you don't need to
 // colocate the entire config).
 React.render((
   <Router history={BrowserHistory}>