message: docs: fix sentence phrasing
  `In this section, you'll add a "Buy" button the product details page.` -> `In this section, you'll add a "Buy" button to the product details page.`
  PR Close
diff: @@ -20,7 +20,7 @@ Services are the place where you share data between parts of your application. F
  Up to this point, users can view product information, and simulate sharing and being notified about product changes. They cannot, however, buy products.
  -In this section, you'll add a "Buy" button the product details page.
  +In this section, you'll add a "Buy" button to the product details page.
  You'll also set up a cart service to store information about products in the cart.
  <div class="alert is-helpful">
  