install.yaml: fix have coherent namespace on tuto
`federation-system` should be used on install.yaml since there is a statefullset inside this config where it should to have correct permission on RBAC.
@@ -121,7 +121,7 @@ supported, along with the service and statefulset for the
federation-controller-manager.
```bash
-kubectl apply --validate=false -f hack/install-latest.yaml
+kubectl -n federation-system apply --validate=false -f hack/install-latest.yaml
```
**NOTE:** The validation fails for harmless reasons on kube >= 1.11 so ignore validation
