doc: document opening hidden files on Windows

PR-URL: https://github.com/nodejs/node/pull/15409
Fixes: https://github.com/nodejs/node/issues/14553


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Nikolai Vavilov <vvnicholas@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>