doc: add richardlau to collaborators

PR-URL: https://github.com/nodejs/node/pull/12020


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>