Update setup-jetstream.md (#2200)

* Update setup-jetstream.md

Added missing information how to create the JetStream. Creating a JetStream is essential. Otherwise the pub/sub for jetstream won't work properly.

Signed-off-by: Armin Schlegel <armin.schlegel@gmx.de>

* Update setup-jetstream.md

Signed-off-by: Armin Schlegel <armin.schlegel@gmx.de>

Co-authored-by: Mark Fussell <markfussell@gmail.com>

daprdocs/content/en/reference/components-reference/supported-pubsub/setup-jetstream.md

@@ -82,6 +82,14 @@ with NATS, find the service with: `kubectl get svc my-nats`.
 
 {{< /tabs >}}
 
+## Create JetStream
+
+It is essential to create a NATS JetStream for a specific subject. For example, for a NATS server running locally use:
+
+```bash
+nats -s localhost:4222 stream add myStream --subjects mySubject
+```
+
 ## Related links
 - [Basic schema for a Dapr component]({{< ref component-schema >}})
 - Read [this guide]({{< ref "howto-publish-subscribe.md#step-2-publish-a-topic" >}}) for instructions on configuring pub/sub components