Update sitemap.mdx (#66668)

added js version of 'localized sitemap', which was missing from the md

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---------

Co-authored-by: JJ Kasper <[email protected]>

docs/02-app/02-api-reference/02-file-conventions/01-metadata/sitemap.mdx

@@ -201,6 +201,43 @@ export default function sitemap(): MetadataRoute.Sitemap {
 }
 ```
 
+```js filename="app/sitemap.js" switcher
+export default function sitemap() {
+  return [
+    {
+      url: 'https://acme.com',
+      lastModified: new Date(),
+      alternates: {
+        languages: {
+          es: 'https://acme.com/es',
+          de: 'https://acme.com/de',
+        },
+      },
+    },
+    {
+      url: 'https://acme.com/about',
+      lastModified: new Date(),
+      alternates: {
+        languages: {
+          es: 'https://acme.com/es/about',
+          de: 'https://acme.com/de/about',
+        },
+      },
+    },
+    {
+      url: 'https://acme.com/blog',
+      lastModified: new Date(),
+      alternates: {
+        languages: {
+          es: 'https://acme.com/es/blog',
+          de: 'https://acme.com/de/blog',
+        },
+      },
+    },
+  ]
+}
+```
+
 Output:
 
 ```xml filename="acme.com/sitemap.xml"