doc: add builtin module in building.md

Fixes: https://github.com/nodejs/node/issues/12516
Refs: https://github.com/nodejs/node/pull/2497

PR-URL: https://github.com/nodejs/node/pull/17705


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>