Update docs/backend-system/core-services/url-reader.md

Signed-off-by: Johan Haals <johan.haals@gmail.com>

Co-authored-by: Fredrik Adelöw <freben@gmail.com>
Signed-off-by: Johan Haals <johan@haals.se>

docs/backend-system/core-services/url-reader.md

@@ -50,8 +50,7 @@ createBackendPlugin({
 
 Custom URL readers that are not intended for open sourcing via a custom service factory for that specific reader. The following example shows how to create a custom URL reader and provide it to the backend.
 
-```ts
-// File: packages/backend/src/index.ts
+```ts title="packages/backend/src/index.ts"
 import { urlReaderFactoriesServiceRef } from '@backstage/backend-defaults/urlReader';
 import {
   createBackendFeatureLoader,