docs: added gift message guide (#12833)

www/apps/resources/sidebars/how-to-tutorials.mjs

@@ -72,6 +72,13 @@ export const howToTutorialsSidebar = [
 
 While tutorials show you a specific use case, they also help you understand how to implement similar use cases in your own projects. Also, you can implement the use case in a tutorial differently to fit your business requirements.`,
     children: [
+      {
+        type: "link",
+        title: "Add Gift Message",
+        path: "/how-to-tutorials/tutorials/gift-message",
+        description:
+          "Learn how to add a gift option and message to items in the cart.",
+      },
       {
         type: "ref",
         title: "Analytics with Segment",