doc: improve AsyncLocalStorage sample

PR-URL: https://github.com/nodejs/node/pull/32757


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>