Joomla plugin - NEW Custom field type in Hikashop

I need to add new Field type in Hikashop->Display->Custom fields menu. New Field type name - "Number". I use table - item. This field type will automatically generate number of item in cart. For example: i'm adding 4 products to cart and this custom item field will add numbers to each products, for first product it will be 1, for second - 2, etc. As much products in cart. So i just need items numbering. You should create plugin in your server and show me how it works and do the install, so i can use it on every site i need.