doc: add sxa as collaborator

Signed-off-by: Stewart Addison <sxa@uk.ibm.com>

PR-URL: #34338
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Gus Caplan <me@gus.host>

Author: Stewart Addison

README.md

@@ -401,6 +401,8 @@ For information about the governance of the Node.js project, see
 **Steven R Loomis** <srloomis@us.ibm.com>
 * [starkwang](https://github.com/starkwang) -
 **Weijia Wang** <starkwang@126.com>
+* [sxa](https://github.com/sxa) -
+**Stewart X Addison** <sxa@uk.ibm.com>
 * [targos](https://github.com/targos) -
 **Michaël Zasso** <targos@protonmail.com> (he/him)
 * [thefourtheye](https://github.com/thefourtheye) -