improved explanation of wildcard expansion

@wking this is the same request I posted against the frozen repo earlier, now against this repo as you requested.

It's a small patch but I still hope it's good enough for the instructor task...

bash typically passes patterns that match nothing as a command line
parameter (as though the pattern had been quoted). Therefore
"mv *.dat original-*.dat" does to "mv basilisk.dat unicorn.dat", but
to "mv basilisk.dat unicorn.dat original-*.dat". (The passing through
of the pattern can be disabled by setting the nullglob option but
that is not set by default.) I've therefore rewritten relevant parts
of parts 03 and 04 to reflect the current typical behaviour.