doc: Update the code example to use the correct App Router syntax (#189)

packages/docs-site/src/pages/other-providers.mdx

@@ -8,6 +8,7 @@ This guide will show you how to use next-S3-upload with non-AWS providers.
 
 First, customize the API route to use the access keys, bucket, region, and endpoint provided by your host. For example, a Digital Ocean Spaces setup may look something like this.
 
+### Pages router
 ```js
 // pages/api/s3-upload.js
 import { APIRoute } from "next-s3-upload";
@@ -21,6 +22,20 @@ export default APIRoute.configure({
 });
 ```
 
+### App router
+```js
+// app/api/s3-upload/route.js
+import { POST as APIRoute } from "next-s3-upload/route";
+
+export const POST = APIRoute.configure({
+  accessKeyId: process.env.DIGITAL_OCEAN_SPACES_KEY,
+  secretAccessKey: process.env.DIGITAL_OCEAN_SPACES_SECRET,
+  bucket: "name-of-bucket",
+  region: "us-east-1",
+  endpoint: "https://nyc3.digitaloceanspaces.com"
+});
+```
+
 The configuration values used here will be different for everyone. Please refer to your provider's documentation for the correct values.
 
 Also, don't forget to setup environment variables for the API keys.