influxdb: add note about configuration

Author: patapenka-alexey

docker-compose.yml

@@ -39,6 +39,8 @@ services:
       INFLUXDB_DB: "metrics"
       INFLUXDB_ADMIN_USER: "admin"
       INFLUXDB_ADMIN_PASSWORD: "admin"
+      # you should specify this manually at grafana data source settings
+      # as `auth` options for `influxdb` source.
       INFLUXDB_USER: "telegraf"
       INFLUXDB_USER_PASSWORD: "telegraf"
       INFLUXDB_HTTP_AUTH_ENABLED: "true"