Improve running steps on README.md

The current steps prevent us from requesting endpoints because the database hasn't been prepared.

Author: otegami

README.md

@@ -15,8 +15,7 @@ A [Grape](http://github.com/ruby-grape/grape) API mounted on Rails.
 ## Run
 
 ```
-bundle install
-rails s
+bin/setup
 ```
 
 - Try http://localhost:3000/api/ping or http://localhost:3000/api/protected/ping with _username_ and _password_.