fix domain example for services

Author: commit111

docs/concepts/domains.mdx

@@ -30,7 +30,7 @@ https://<username>-<service-name>--<port>.defang.dev
 If you're using [Defang BYOC](./defang-byoc.md), your domain will be:
 
 ```
-https://<service-name>--<port>.<username>.defang.app
+https://<service-name>--<port>.<project-name>.<username>.defang.app
 ```
   </TabItem>
 </Tabs>