doc: add user to useStateValue and conditional rendering

src/Checkout/Checkout.js

@@ -8,7 +8,7 @@ import CheckoutProduct from "./CheckoutProduct";
 import "./Checkout.css";
 
 function Checkout() {
-  const [{ basket }, dispatch] = useStateValue();
+  const [{ basket, user }, dispatch] = useStateValue();
   return (
     <section className="checkout">
       <article className="checkout__left">
@@ -19,6 +19,7 @@ function Checkout() {
         />
 
         <article>
+          {!user ? "" : <h3>Hello, {!user?.email}</h3>}
           <h2 className="checkout__title">Your Shopping Basket</h2>
           {basket.map((item) => (
             <CheckoutProduct