Adding quantity to cart items
The problem that we've got right now is if you add the same item to the cart more than once, it prints out mulitple times. [add the same item to the cart multiple times]
How a shopping cart usually works, is, an individual item is just displayed once, but a quantity is displayed.
If we look at the completed version that's exactly how that works. [demonstrate adding the same item multiple times on the finished product]