我希望订单嵌套在用户中,所以我可以有这些路由：
/users /users/:id /users/:id/new /users/:id/edit /users/:user_id/orders /users/:user_id/orders/:id /users/:user_id/orders/:id/new /users/:user_id/orders/:id/edit
我如何用activeadmin？
ActiveAdmin.register Order do belongs_to :user end
