doc: update tools/doc/README.md

PR-URL: https://github.com/nodejs/node/pull/20047


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>