More details on how to customize from inside an application

[schof]

Ran into a lot of confusion when trying to walk somebody through how to do simple controller decorator in their stand alone application (NOTE: not an extension) w/Spree.

https://gist.github.com/schof/5560963

Needed to do something like:

  mount Spree::Core::Engine, :at => '/'

  Spree::Core::Engine.routes.prepend do
    namespace :admin do
      get '/products/import' => "products#import", :as => :products_import
    end
  end

which was unexpected. We should document the prepend/append stuff for when adding routes to spree namespace.