Update the definition of the Z pack format code

[27pchrisl]

a and Z had the same definition, but Z is the NUL-terminated variation.

[nielsdos]

It's actually NUL terminated, and padded in some cases: https://3v4l.org/WGYGn
Not sure how to communicate this in the best way

[27pchrisl]

Perl’s doc says “A null-terminated (ASCIZ) string, will be null padded.”, that seems clear? https://perldoc.perl.org/functions/pack. - could use their definition for A as well to make the distinction

[nielsdos]

Yes that description is better

[27pchrisl]

I've updated the description. I did look at the A description as well, but I think it's clear enough as it is.

[nielsdos]

Thanks