add missing js code block descriptor

README.md

@@ -569,7 +569,7 @@ Ember Simple Auth works with engines out of the box. The host app and any
 engine(s) share the same `session` service so they can synchronize the
 authentication status:
 
-```
+```js
 // my-engine/addon/routes/index.js
 import Application from '@ember/application';
 import loadInitializers from 'ember-load-initializers';