docs: add note on NATS jetstream beta package (ThreeDotsLabs#405)

Co-authored-by: Miłosz Smółka <[email protected]>

docs/content/pubsubs/nats.md

@@ -12,6 +12,11 @@ toc = false
 
 NATS Jetstream is a data streaming system powered by NATS, and written in the Go programming language.
 
+As of v2.0.2 this middleware will contain a beta implementation in `pkg/jetstream` based on the 
+[nats.go Jetstream package](https://github.com/nats-io/nats.go/tree/main/jetstream). This implementation is 
+considered experimental tracking with the upstream client though we target a stable watermill API by v2.1.  
+For production use it is recommended to use the pubsub implementations in `pkg/nats` with Jetstream enabled.
+
 ### Installation
 
     go get github.com/ThreeDotsLabs/watermill-nats/v2
@@ -63,7 +68,7 @@ Example:
 {{% load-snippet-partial file="src-link/_examples/pubsubs/nats-jetstream/main.go" first_line_contains="subscriber, err :=" last_line_contains="panic(err)" padding_after="1" %}}
 {{% /render-md %}}
 
-You can also use `NewSubscriberWithNATSConn` and `NewPublisherWithNatsConn` to use a custom `stan.Conn` created by `NewStanConnection`.
+You can also use `NewSubscriberWithNatsConn` and `NewPublisherWithNatsConn` to use a custom `*nats.Conn`.
 
 #### Publishing