Add solution to product inventory

Author: Karan Goel

README.md

@@ -141,7 +141,7 @@ Networking
 Classes
 ---------
 
-**Product Inventory Project** - Create an application which manages an inventory of products. Create a product class which has a price, id, and quantity on hand. Then create an *inventory* class which keeps track of various products and can sum up the inventory value.
+[**Product Inventory Project**](https://github.com/thekarangoel/Projects/blob/master/Classes/product_inventory.py) - Create an application which manages an inventory of products. Create a product class which has a price, id, and quantity on hand. Then create an *inventory* class which keeps track of various products and can sum up the inventory value.
 
 **Airline / Hotel Reservation System** - Create a reservation system which books airline seats or hotel rooms. It charges various rates for particular sections of the plane or hotel. Example, first class is going to cost more than coach. Hotel rooms have penthouse suites which cost more. Keep track of when rooms will be available and can be scheduled.