docs: generate invoice tutorial (#13077)

* docs: generate invoice tutorial

* fix vale error

* add missing icon

* fix sidebar

* update date

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

@@ -114,6 +114,13 @@ While tutorials show you a specific use case, they also help you understand how
         description:
           "Learn how to implement first-purchase discounts in your Medusa store.",
       },
+      {
+        type: "link",
+        title: "Generate Invoices",
+        path: "/how-to-tutorials/tutorials/invoice-generator",
+        description:
+          "Learn how to generate invoices for orders in your Medusa store.",
+      },
       {
         type: "link",
         title: "Loyalty Points System",