docs: update README to clarify client IP preservation with Traefik and HelmChartConfig

README.md

@@ -128,14 +128,31 @@ curl -si "http://<node-ip>/"
 
 By default the app sees a cluster-internal address (for example `10.42.0.1`)
 instead of the real client IP, because the Traefik Service runs with
-`externalTrafficPolicy: Cluster`. To preserve the client IP, apply
-[k3s/traefik-config.yaml](k3s/traefik-config.yaml), which sets
-`externalTrafficPolicy: Local` on the Traefik Service:
+`externalTrafficPolicy: Cluster`. To preserve the client IP, set
+`externalTrafficPolicy: Local` on the Traefik Service through a
+`HelmChartConfig`, as in [k3s/traefik-config.yaml](k3s/traefik-config.yaml).
+
+A cluster can hold only one `HelmChartConfig` named `traefik`, so first check
+whether one already exists:
+
+```bash
+kubectl get helmchartconfig traefik -n kube-system
+```
+
+If it does not exist, apply the file as is:
 
 ```bash
 kubectl apply -f k3s/traefik-config.yaml
 ```
 
+If it already exists, do not apply the file, as it would replace the existing
+Traefik settings. Instead, add `externalTrafficPolicy: Local` under the
+`service.spec` section of the existing `valuesContent`:
+
+```bash
+kubectl edit helmchartconfig traefik -n kube-system
+```
+
 #### Option 2: ServiceLB
 
 k3s also includes the ServiceLB load balancer. The single `LoadBalancer`