doc: document fs.watchFile() bigint option

This commit documents the bigint option to fs.watchFile(), which
has been supported since v10.5.0.

PR-URL: https://github.com/nodejs/node/pull/32128


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>