docs: fix add custom domain

docs/add-custom-domain-using-traefik.md

@@ -1,4 +1,4 @@
-Add following labels to *-nginx service
+Add following labels to `frontend` service
 
 ```yaml
   - "traefik.http.routers.custom-domain.rule=Host(`custom.localhost`)"
@@ -15,28 +15,16 @@ Example:
 
 ```yaml
 frontend:
-  image: frappe/erpnext-nginx:${ERPNEXT_VERSION}
+  ...
-  restart: on-failure
-  environment:
-    - FRAPPE_PY=erpnext-python
-    - FRAPPE_PY_PORT=8000
-    - FRAPPE_SOCKETIO=frappe-socketio
-    - SOCKETIO_PORT=9000
   labels:
-    - "traefik.enable=true"
+    ...
-    - "traefik.http.routers.frontend.rule=Host(${SITES})"
     - "traefik.http.routers.custom-domain.rule=Host(`custom.localhost`)"
     - "traefik.http.routers.custom-domain.entrypoints=web"
     - "traefik.http.middlewares.custom-domain.headers.customrequestheaders.Host=mysite.localhost"
     - "traefik.http.routers.custom-domain.middlewares=custom-domain"
     # Add following header only if TLS is needed in case of live server
     - "traefik.http.routers.custom-domain.tls.certresolver=myresolver"
-    - "${ENTRYPOINT_LABEL}"
+    ...
-    - "${CERT_RESOLVER_LABEL}"
-    - "traefik.http.services.frontend.loadbalancer.server.port=80"
-  volumes:
-    - sites-vol:/var/www/html/sites:rw
-    - assets-vol:/assets:rw
 ```
 
 This will add `custom.localhost` as custom domain for `mysite.localhost`