doc: add myself to list of TSC members

PR-URL: #20132
Fixes: nodejs/TSC#485
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: TimothyGu

README.md

@@ -264,6 +264,8 @@ For more information about the governance of the Node.js project, see
 **Michaël Zasso** <targos@protonmail.com> (he/him)
 * [thefourtheye](https://github.com/thefourtheye) -
 **Sakthipriyan Vairamani** <thechargingvolcano@gmail.com> (he/him)
+* [TimothyGu](https://github.com/TimothyGu) -
+**Tiancheng "Timothy" Gu** <timothygu99@gmail.com> (he/him)
 * [Trott](https://github.com/Trott) -
 **Rich Trott** <rtrott@gmail.com> (he/him)