util-linux: add hd symlink for hexdump --canonical
As mentioned in the man page, `hd` is a shorthand for `hexdump
--canonical`. Shell completion (at least in bash) works without any
additional modifications.
In nixpkgs, hd is offered by busybox but not util-linux so far. Other
distros, such as Debian make hd available through a similar
implementation[1].
[1]: https://salsa.debian.org/debian/util-linux/-/blob/4ccecb3e6d53fc7990d8287f9e00b3be6a64f209/debian/bsdextrautils.links
