Refer to sysutils/cdrtools instead of sysutils/mkisofs now that the
mkisofs port was merged into cdrtools. I've also replaced most of the
references to the <filename role="package">mkisofs</filename> program
with an entity which we already have.

PR: docs/69087
Submitted by: Janos Mohasci <janos.mohasci@bsd.hu>