ActiveAdmin custom menu links

active_admin.rb

# config/initializers/active_admin.rb
ActiveAdmin.setup do |config|
  config.namespace :admin do |admin|
    admin.build_menu do |menu|
      menu.add :label => "The Application", :url => "/", :priority => 0

      menu.add :label => "Sites" do |sites|
        sites.add :label => "Google", :url => "http://google.com", :html_options => { :target => :blank }
        sites.add :label => "Facebook", :url => "http://facebook.com"
        sites.add :label => "Github", :url => "http://github.com"
      end
    end
  end
end