doc: add missing hash for header link

The link is to a heading in the file, but is missing the #

PR-URL: https://github.com/nodejs/node/pull/30188


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>