Add method foreachAsync to Sink object

akka-docs/src/test/scala/docs/stream/SinkRecipeDocSpec.scala

@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2018 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream
+
+import akka.stream.scaladsl.{ Sink, Source }
+import docs.stream.cookbook.RecipeSpec
+
+import scala.concurrent.Future
+
+class SinkRecipeDocSpec extends RecipeSpec {
+  "Sink.foreachAsync" must {
+    "processing each element asynchronously" in {
+      def asyncProcessing(value: Int): Future[Unit] = Future { println(value) }(system.dispatcher)
+      //#forseachAsync-processing
+      //def asyncProcessing(value: Int): Future[Unit] = _
+
+      Source(1 to 100)
+        .runWith(Sink.foreachAsync(10)(asyncProcessing))
+      //#forseachAsync-processing
+    }
+  }
+}