Add information to the Wiki about how to remove group name

[ddowse]

To remove a obsolete group name e.g offsite1 use zfs-inherit(8) without a value to the group name.

zfs inherit autobackup:offsite1 rpool

This is just a draft. Improve the text to your liking.

[psy0rz]

thanks, i added it: https://github.com/psy0rz/zfs_autobackup/wiki#select-filesystems-to-backup