doc: add note about debugging worker_threads

PR-URL: #30594
Fixes: #30197
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

doc/api/debugger.md

@@ -197,5 +197,10 @@ debugging sessions.)
 If the Chrome browser is older than 66.0.3345.0,
 use `inspector.html` instead of `js_app.html` in the above URL.
 
+Chrome DevTools doesn't support debugging [Worker Threads][] yet.
+[ndb][] can be used to debug them.
+
 [Chrome DevTools Protocol]: https://chromedevtools.github.io/devtools-protocol/
 [V8 Inspector]: #debugger_v8_inspector_integration_for_node_js
+[Worker Threads]: worker_threads.html
+[ndb]: https://github.com/GoogleChromeLabs/ndb/