doc: dedupe links

Replace some repeated full links
with concise ones and bottom references.

PR-URL: https://github.com/nodejs/node/pull/18213


Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>