This improves usability a little as we no longer require using touch.
Also reword the manpage wrt. parameters and fix usage() [1]
With no media in a cd(4) drive, the reads will loop producing EINVAL,
abort in that case [2].
Document the shortcoming of sectorsize and MAXPHYS (a quick solution
to this might be having MAXPHYS as the "bigsize", in short testing it
didn't make a difference on throughput).
Submitted by: arundel [1]
PR: bin/154528 [2]
93c5246832