doc: describe how to update zlib

See:
- https://github.com/nodejs/node/pull/31201

PR-URL: https://github.com/nodejs/node/pull/31800


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>