Feature: Add more pizzas

[HadikaMalik]

From React-Module-Project created by SallyMcGrath: CodeYourFuture#10

Dependent ticket: complete and merge #9 before starting this ticket

Instructions:

In the <Restaurant /> component, create a new function named orderOne. The orderOne function doesn't take any parameters and should use the setOrders function to increment the orders state variable by 1. Then, add a onClick handler to the Add <button> that calls the orderOne function when it's being clicked.

Test:

When the Add button is clicked, the number of pizzas increases by 1