Adding Channel to documentation

site/concurrency-primitives.md

@@ -3,12 +3,31 @@
 In the [`fs2.concurrent` package](https://github.com/functional-streams-for-scala/fs2/blob/series/1.0/core/shared/src/main/scala/fs2/concurrent/) you'll find a bunch of useful concurrency primitives built on the concurrency primitives defined in `cats-effect`. For example:
 
 - `Topic[F, A]`
+- `Channel[F, A]`
 - `Signal[F, A]`
 
 In addition, `Stream` provides functions to interact with cats-effect's `Queue`. 
 
 ## Simple Examples
 
+### Channel
+`Channel` implements a publish-subscribe pattern and is particularly useful where we have multiple `publishers` and a single `subscriber`. In the following example, we have two streams, `pub1` and `pub2` publishing the strings `"Hello"` and `"World"` every `1` and `2` seconds respectively. Additionally, we have `sub`, a subscriber that consumes and prints each element. The three streams are then run in parallel and interrupted after `6` seconds.
+
+```scala mdoc:silent
+import cats.effect._
+import fs2.Stream
+import scala.concurrent.duration._
+import cats.effect.unsafe.implicits.global
+import fs2.concurrent.Channel
+
+Channel.unbounded[IO, String].flatMap{channel =>
+  val pub1 = Stream.repeatEval(IO("Hello")).evalMap(channel.send).metered(1.second)
+  val pub2 = Stream.repeatEval(IO("World")).evalMap(channel.send).metered(2.seconds)
+  val sub = channel.stream.evalMap(IO.println)
+  Stream(pub1, pub2, sub).parJoinUnbounded.interruptAfter(6.seconds).compile.drain
+}.unsafeRunSync()
+```
+
 ### Topic
 
 (based on [Pera Villega](https://perevillega.com/)'s example [here](https://underscore.io/blog/posts/2018/03/20/fs2.html))