doc: clear up child_process command resolution

Fixes: https://github.com/nodejs/node/issues/20605
Refs: https://github.com/libuv/libuv/pull/1837

PR-URL: https://github.com/nodejs/node/pull/32091


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Bartosz Sosnowski <bartosz@janeasystems.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>