Add a note about multiple Pub/Sub channel listeners (#2433)

* Add multiple listener language to pub/sub docks

Clarify that multiple subscriptions create multiple listeners.

* Update pub-sub.md

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Co-authored-by: Leibale Eidelman <me@leibale.com>

docs/pub-sub.md

@@ -39,6 +39,8 @@ await client.pSubscribe('channe*', listener);
 await client.sSubscribe('channel', listener);
 ```
 
+> ⚠️ Subscribing to the same channel more than once will create multiple listeners which will each be called when a message is recieved.
+
 ## Publishing
 
 ```javascript