doc: edit addon text about event loop blocking

PR-URL: https://github.com/nodejs/node/pull/36448


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>