clarify Models user guide
clarify Models user guide

Inform the $useAutoIncrement default value (which is 'true'), so developers would be aware of that option if they don't use auto-incremented INT's on primary keys, especially when triggering an 'afterInsert' event which will eventually cause the $data['id'] value to be 0 instead of the actual primary key (see 'system/Model.php' line 254 : https://github.com/codeigniter4/CodeIgniter4/blob/622d50aa2976b85f7cb1479faec7558cd9ec2341/system/Model.php#L254)
kenjis/CodeIgniter4,kenjis/CodeIgniter4,kenjis/CodeIgniter4,kenjis/CodeIgniter4,kenjis/CodeIgniter4