docs: add references to punycode.md

Add references to related `url` functions in punycode.md. These provide
guidance to users who may be investigating the punycode module for URL
encoding.

PR-URL: #36761
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Yash Ladha <yash@yashladha.in>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/punycode.md

@@ -12,7 +12,9 @@ deprecated: v7.0.0
 **The version of the punycode module bundled in Node.js is being deprecated**.
 In a future major version of Node.js this module will be removed. Users
 currently depending on the `punycode` module should switch to using the
-userland-provided [Punycode.js][] module instead.
+userland-provided [Punycode.js][] module instead. For punycode-based URL
+encoding, see [`url.domainToASCII`][] or, more generally, the
+[WHATWG URL API][].
 
 The `punycode` module is a bundled version of the [Punycode.js][] module. It
 can be accessed using:
@@ -150,3 +152,5 @@ Returns a string identifying the current [Punycode.js][] version number.
 
 [Punycode]: https://tools.ietf.org/html/rfc3492
 [Punycode.js]: https://github.com/bestiejs/punycode.js
+[WHATWG URL API]: url.md#url_the_whatwg_url_api
+[`url.domainToASCII`]: url.md#url_url_domaintoascii_domain