Fix formatting of placeholder in README.md for custom URL

Author: AnatoliB

samples-v2/openai_agents/customer_service/README.md

@@ -28,7 +28,7 @@ python customer_service_client.py
 If your function app is running on a different host or port, you can specify a custom URL:
 
 ```bash
-python customer_service_client.py --start-url http://<app host URL>/api/orchestrators/customer_service
+python customer_service_client.py --start-url http://<app-host-URL>/api/orchestrators/customer_service
 ```
 
 The client will: