Update .env.docker to clarify InfluxDB token setup instructions

backend/.env.docker

@@ -2,6 +2,8 @@
 INFLUXDB_URL=http://influxdb2:8086
 INFLUXDB_ORG=docs
 INFLUXDB_BUCKET=co2-test
+# !!! replace Token with your own token !!! - you can create a new token in the InfluxDB UI
+# more info in readme.md
 INFLUXDB_TOKEN=xHpy7Vdt2_3hNb9DOpc1DHO6UkH19R58_okbCORz5vhDvYaiYJN2e0tl2H4rQlym6w5dCbRweeMWL00DU2ymNw==
 # MQTT config
 MQTT_BROKER_URL=mosquitto-broker