doc: add refack to collaborators

PR-URL: #12277
Refs: https://github.com/nodejs/node/blob/master/doc/onboarding.md
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>

Author: refack

Diff for: README.md

@@ -325,6 +325,8 @@ more information about the governance of the Node.js project, see
 **Prince John Wesley** <princejohnwesley@gmail.com>
 * [qard](https://github.com/qard) -
 **Stephen Belanger** <admin@stephenbelanger.com> (he/him)
+* [refack](https://github.com/refack) -
+**Refael Ackermann** <refack@gmail.com> (he/him)
 * [richardlau](https://github.com/richardlau) -
 **Richard Lau** <riclau@uk.ibm.com>
 * [rlidwka](https://github.com/rlidwka) -