mkarchroot: Added default pacman cache in usage help

	echo '    -C <file>     Location of a pacman config file'

	echo '    -M <file>     Location of a makepkg config file'

	echo '    -n            Do not copy config files into the chroot'

	echo "    -c <dir>      Set pacman cache. Default: ${cache_dir}"

	echo "    -c <dir>      Set pacman cache. Default: /var/cache/pacman/pkg"

	echo '    -h            This message'

	exit $1

}