message: add comment about redis url
diff: @@ -28,4 +28,7 @@ url = "http://influxdb:8086"
  db = "metrics"
  [redis]
  -url = "redis://redis-master"
  +# The url is configured via the enviroment variable `XAYNET_REDIS__URL`.
  +# `XAYNET_REDIS__URL` depends on the enviroment variable `REDIS_AUTH`,
  +# which is defined as a Kubernetes secret and exposed to the coordinator pod.
  +# See: k8s/coordinator/base/deployment.yaml
  