doc: explain Worker semantics in async_hooks.md

PR-URL: #20876
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Shingo Inoue <leko.noor@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: John-David Dalton <john.david.dalton@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>

doc/api/async_hooks.md

@@ -21,6 +21,9 @@ A resource can also be closed before the callback is called. `AsyncHook` does
 not explicitly distinguish between these different cases but will represent them
 as the abstract concept that is a resource.
 
+If [`Worker`][]s are used, each thread has an independent `async_hooks`
+interface, and each thread will use a new set of async IDs.
+
 ## Public API
 
 ### Overview
@@ -224,7 +227,7 @@ clearTimeout(setTimeout(() => {}, 10));
 ```
 
 Every new resource is assigned an ID that is unique within the scope of the
-current process.
+current Node.js instance.
 
 ###### `type`
 
@@ -725,3 +728,4 @@ never be called.
 [Hook Callbacks]: #async_hooks_hook_callbacks
 [PromiseHooks]: https://docs.google.com/document/d/1rda3yKGHimKIhg5YeoAmCOtyURgsbTH_qaYR79FELlk
 [promise execution tracking]: #async_hooks_promise_execution_tracking
+[`Worker`]: worker.html#worker_worker