Changing Readme to include requirement of i18n

In the topic Rails app without Asset Pipeline `i18n.js` is loaded along with the `translations.js` file. (`<%= javascript_include_tag "i18n", "translations" %>`). 

In the Rails app with Asset Pipeline the instructions tell to only load `i18n/translations`. You should load before the `i18n` with the `//= require i18n` directive. 

I don't now if this is on purpose (like every rails guy should now this) bu it wasn't clear for a noob like me ;)