docs: fix spelling and grammar (#13862)

Fixed various spelling errors and grammatical issues across multiple .mdx documentation files.

www/apps/resources/app/storefront-development/guides/express-checkout/page.mdx

@@ -1440,7 +1440,7 @@ const handleAddToCart = () => {
 
 You add a `handleAddToCart` function that first checks that a variant is selected, that it's in stock, and that the customer has set a quantity greater than `0`.
 
-If the conditions are satisifed, you set `loading` to `true`, then call the `addToCart` function from the cart context, passing the selected variant's ID and the quantity as arguments.
+If the conditions are satisfied, you set `loading` to `true`, then call the `addToCart` function from the cart context, passing the selected variant's ID and the quantity as arguments.
 
 After the product is added to the cart, you navigate to the address step, which you'll create later.