Inspired by the commit message introducing beinstall.sh: https://reviews.freebsd.org/rS302977.
igor, mandoc: OK
@krion, @mat, may I ask you for an approval to commit these changes?
We generally document shutdown(8) instead of reboot(8). Even the latter man page suggestions using `shutdown.
I've opened a new revision: https://reviews.freebsd.org/D16843