doc: revise security-reporting example text

Edit for simplicity and clarity.

PR-URL: https://github.com/nodejs/node/pull/23759


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>