Update sink README.md

sinks/README.md

@@ -16,8 +16,50 @@ Nothing to do, all sinks are pure Go code
 A sink contains three functions and is derived from the type `Sink` (in `metricSink.go`):
 * `Init(config SinkConfig) error`
 * `Write(measurement string, tags map[string]string, fields map[string]interface{}, t time.Time) error`
+* `Flush() error`
 * `Close()`
 
-The data structures should be set up in `Init()` like opening a file or server connection. The `Write()` function takes a measurement, tags, fields and a timestamp and writes/sends the data. The `Close()` function should tear down anything created in `Init()`.
+The data structures should be set up in `Init()` like opening a file or server connection. The `Write()` function takes a measurement, tags, fields and a timestamp and writes/sends the data. For non-blocking sinks, the `Flush()` method tells the sink to drain its internal buffers. The `Close()` function should tear down anything created in `Init()`.
 
-Finally, the sink needs to be registered in the `metric-collector.go`. There is a list of sinks called `Sinks` which is a map (string -> pointer to sink). Add a new entry with a descriptive name and the new sink.
+Finally, the sink needs to be registered in the `metric-collector.go`. There is a list of sinks called `Sinks` which is a map (sink_type_string -> pointer to sink). Add a new entry with a descriptive name and the new sink. Afterwards, it can be configured in the main configuration file at `type`:
+
+```json
+{
+  "sink": {
+    "user": "testuser",
+    "password": "testpass",
+    "host": "127.0.0.1",
+    "port": "9090",
+    "database": "testdb",
+    "organization": "testorg",
+    "ssl": false
+    "type": "stdout"
+  }
+}
+```
+# Sink configuration
+
+## `stdoutSink`
+When configuring `type = stdout`, all metrics are printed to stdout. No further configuration is required or touched, so you can leave your other-sink-config in there and just change the `type` for debugging purposes
+
+## `influxSink`
+The InfluxDB sink uses blocking write operations to write to an InfluxDB database using the v2 API. It uses the following configuration options:
+* `host`: Hostname of the database instance
+* `port`: Portnumber (as string) of the database
+* `database`: Name of the database, called 'bucket' in InfluxDB v2
+* `organization`: The InfluxDB v2 API uses organizations to separate database instances running on the same host
+* `ssl`: Boolean to activate SSL/TLS
+* `user`: Although the v2 API uses API keys instead of username and password, this field can be used if the sink should authentificate with `username:password`. If you want to use an API key, leave this field empty.
+* `password`: API key for the InfluxDB v2 API or password if `user` is set
+
+## `natsSink`
+* `host`: Hostname of the NATS server
+* `port`: Portnumber (as string) of the NATS server
+* `user`: Username for authentification in the NATS transport system
+* `password`: Password for authentification in the NATS transport system
+
+## `httpSink`
+* `host`: Hostname of the HTTP server
+* `port`: Portnumber (as string) of the HTTP server
+* `database`: Endpoint to write to. HTTP POST requests are performed on `http://<host>:<port>/<database>`
+* `password`: JSON Web token used for authentification