Add documentation for the sink.

README.md

@@ -23,6 +23,7 @@ It's worth familiarising yourself with [Sequence numbers and Sub sequence number
     * [Usage: Producer](#usage-usage-producer)
         * [Actor Based Implementation](#usage-usage-producer-actor-based-implementation)
         * [Pure Scala based implementation (simple wrapper around KPL)](#usage-usage-producer-pure-scala-based-implementation-simple-wrapper-around-kpl)
+        * [Akka Stream Sink](#akka-stream-sink)
 * [Running the reliability test](#running-the-reliability-test)
     * [Delete & recreate kinesisstreams and dynamo table](#running-the-reliability-test-delete-recreate-kinesisstreams-and-dynamo-table)
     * [Running the producer-consumer test](#running-the-reliability-test-running-the-producer-consumer-test)
@@ -484,6 +485,55 @@ callback onFailure {
 }
 ```
 
+<a name="akka-stream-sink"></a>
+### Akka Stream Sink
+
+An Akka `Sink` is provided which can be used to publish messages via streams. 
+Every message is send as `ProduserEvent` to the `Sink`, which defines the PartitionKey as well as the payload.
+The `Sink` is created from a `ProducerConf` or directly with a `KinesisProducerActor`. See [Kinesis](https://github.com/WW-Digital/reactive-kinesis/blob/master/src/main/scala/com/weightwatchers/reactive/kinesis/stream/Kinesis.scala)  for the various options.
+
+The `Sink` expects an acknowledgement for every messages send to Kinesis. 
+An amount of unacknowledged messages can be configured, before back pressure is applied.
+See the throttling conf for defining this configuration value.
+Please note: a default value (1000 messages) is applied, if throttling is not configured.
+
+The provided `Sink` produces a `Future[Done]` as materialized value.
+This future succeeds, if all messages from upstream are send to Kinesis and acknowledged.
+It fails if a message could not be send to Kinesis or upstream fails.
+
+```scala
+import akka.stream.scaladsl.Source
+import com.weightwatchers.reactive.kinesis.models._
+import com.weightwatchers.reactive.kinesis.stream._
+
+Source(1.to(100).map(_.toString))
+  .map(num => ProducerEvent(num, num))
+  .runWith(Kinesis.sink("producer-name"))
+  .onComplete {
+    case Success(_) => println("All messages are published successfully.")
+    case Failure(ex) => println(s"Failed to publish messages: ${ex.getMessage}")
+  }
+```
+
+A long running flow can be easily achieved using a `SourceQueue`.
+In this case the flow stays open as long as needed.
+New elements can be published via the materialized queue:
+
+```scala
+import akka.stream.scaladsl.Source
+import com.weightwatchers.reactive.kinesis.models._
+import com.weightwatchers.reactive.kinesis.stream._
+
+val sourceQueue = Source.queue[ProducerEvent](1000, OverflowStrategy.fail)
+  .toMat(Kinesis.sink("producer-name"))(Keep.left)
+  .run()
+
+sourceQueue.offer(ProducerEvent("foo", "bar"))
+sourceQueue.offer(ProducerEvent("foo", "baz"))
+```
+
+The `Sink` uses a `KinesisProducerActor` under the cover. All rules regarding this actor also apply for the `Sink`.  
+
 
 <a name="running-the-reliability-test"></a>
 # Running the reliability test