doc: clarify async iterator leak

Clarifies that creating multiple async iterators from the same stream
can lead to event listener leak.

PR-URL: nodejs#28997
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

doc/api/stream.md

@@ -2502,6 +2502,9 @@ and async iterators are provided below.
 })();
 ```
 
+Async iterators register a permanent error handler on the stream to prevent any
+unhandled post-destroy errors.
+
 #### Creating Readable Streams with Async Generators
 
 We can construct a Node.js Readable Stream from an asynchronous generator