doc: update Grafana instructions

Add note about InfluxDb version. Update authentication instructions.

README.md

@@ -53,7 +53,11 @@ Remember to click "Submit" to save your configuration!
 
 ## Configuring the Grafana Data Source
 
-While technically not in the scope of this plugin, this section describes how to set up an InfluxDB data source in Grafana. (Another option would be to use the experimental [signalk-grafana data](https://github.com/tkurki/signalk-grafana) data source.)
+While technically not in the scope of this plugin, this section describes how to set up an InfluxDB data source in Grafana. (Another option would be to use the experimental [signalk-grafana data](https://github.com/tkurki/signalk-grafana) data source.) These settings have been tested with InfluxDB 2.7.10, earlier versions may or may not work.
+
+These instuctions configure an InfluxDb datasource using InfluxQL as the query language against InfluxDb version 2. InfluxQL is a good choice as the query language because the Grafana datasource includes a UI for building queries by picking database fields instead of manually writing the raw query.
+
+To begin with you will need to [create an API token in InfluxDB](https://docs.influxdata.com/influxdb/v2/admin/tokens/create-token/).
 
 Login to Grafana. On Signal K installations, Grafana often runs on port 3001: http://mysignalkhostname:3001/
 
@@ -65,19 +69,15 @@ Create the data source:
   - Query language: InfluxQL
   - HTTP URL: http://localhost:8086
 
-To authenticate, you need to add a custom HTTP header:
-
-- Header: Authorization
-- Value: Token (token you created when configuring InfluxDB)
-
-Use the following settings:
+Use the following InfluxDB Details:
 
-- Database: (your bucket name)
-- HTTP Method: GET
-- Min time interval: 1s
+- Database: `your bucket name`
+- User: `your influxdb user`
+- Password: `your API Token`
+- HTTP Method: either `GET` or `POST`
 
 Then click "Save & test".
-After a short while, you should get a positive acknowledgment. Now, you can create dashboard panels that use InfluxDB as the data source.
+You should get a positive acknowledgment. Now, you can create dashboard panels that use InfluxDB as the data source.
 
 # History API
 

docker-compose.yml

@@ -2,7 +2,7 @@ version: '2'
 services:
   influxdb:
     container_name: influx2
-    image: "influxdb:2.3"
+    image: "influxdb:2.7.10"
     ports:
      - "8086:8086"
     volumes: