Hi there,
I like to do these things at the command line:
security login create -user-or-group-name "domainname\ROGroup" -application http -role readonly -vserver svm_95_nas -authentication-method domain
You may want to do multiple entries for the application modifier if you want them to have access other methods as well, typically "http, ontapi, ssh".
Then add those users to the AD Group called "ROGroup" or whatever you call it in your domain.