doc: update behaviour of fs.writeFile

As per the decision in https://github.com/nodejs/node/issues/23433,
the `fs.writeFile` will always write from the current position if it
is used with file descriptors. This patch updates it.

Ref: https://github.com/nodejs/node/pull/23709

PR-URL: https://github.com/nodejs/node/pull/25080


Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>