create active_admin_example Rails application

create_active_admin_example.sh

rails new active_admin_example
rake db:create
rails g controller products index
rails g model product name:string description:text price:float
rails g model user first_name:string last_name:string
rails g model order user_id:integer
rails g model order_item order_id:integer product_id:integer quantity:integer
rake db:migrate