$conf['authtype'] = 'authad';
$conf['superuser'] = '@MyAdminGroup';
$conf['plugin']['authad']['account_suffix'] = '@yourdomain.tld';
$conf['plugin']['authad']['base_dn'] = 'DC=yourdomain,DC=tld';
$conf['plugin']['authad']['domain_controllers'] = 'dc1.yourdomain.tld,123.123.123.123';
In line 2, add your AD group name which holds the admin users; replace every space with an underscore and keep the @ at the start.
In line 3, replace yourdomain.tld with your domainname, i.e. example.org or my.example.org
In line 4, for every piece of your domain, add a DC=, i.e. DC=my,DC=example,DC=org
In line 5, enter one or more DCs seperated by a comma. You can enter hostnames or IP addresses.