async_hooks: add migration note

doc/api/async_hooks.md

@@ -2,7 +2,10 @@
 
 <!--introduced_in=v8.1.0-->
 
-> Stability: 1 - Experimental
+> Stability: 1 - Experimental. We plan to remove this API
+> in the future; it will never become stable.
+> Please migrate to [`AsyncLocalStorage`][], [Diagnostics Channel][], and
+> other stable APIs.
 
 <!-- source_link=lib/async_hooks.js -->
 
@@ -864,6 +867,7 @@ The documentation for this class has moved [`AsyncResource`][].
 The documentation for this class has moved [`AsyncLocalStorage`][].
 
 [DEP0111]: deprecations.md#dep0111-processbinding
+[Diagnostics Channel]: diagnostics_channel.md
 [Hook Callbacks]: #hook-callbacks
 [PromiseHooks]: https://docs.google.com/document/d/1rda3yKGHimKIhg5YeoAmCOtyURgsbTH_qaYR79FELlk/edit
 [`AsyncLocalStorage`]: async_context.md#class-asynclocalstorage