Add missing files to README (facebook#2334)

* add missing files

* Update README.md

Author: jesselpalmer

README.md

@@ -65,13 +65,15 @@ my-app/
   public/
     favicon.ico
     index.html
+    manifest.json
   src/
     App.css
     App.js
     App.test.js
     index.css
     index.js
     logo.svg
+    registerServiceWorker.js
 ```
 
 No configuration or complicated folder structures, just the files you need to build your app.<br>