doc: add gireeshpunathil to collaborators

PR-URL: #13967
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

Author: gireeshpunathil

Diff for: README.md

@@ -282,6 +282,8 @@ more information about the governance of the Node.js project, see
 **Wyatt Preul** <wpreul@gmail.com>
 * [gibfahn](https://github.com/gibfahn) -
 **Gibson Fahnestock** <gibfahn@gmail.com> (he/him)
+* [gireeshpunathil](https://github.com/gireeshpunathil) -
+**Gireesh Punathil** <gpunathi@in.ibm.com> (he/him)
 * [iarna](https://github.com/iarna) -
 **Rebecca Turner** <me@re-becca.org>
 * [imran-iq](https://github.com/imran-iq) -