doc: add descriptions about when `options.mode` is ignored

PR-URL: https://github.com/nodejs/node/pull/39881
Fixes: https://github.com/nodejs/node/issues/39859


Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>