There's no need for a "addgroup" or "groupadd" command when:

Does the trick just fine.

That's the beauty in UNIX. If you can edit a text file, you can configure the OS. No "regedit" or anything obscure like that.

As an aside, I usually use "vipw" to add users to my system (rather than the supplied "adduser" script or anything else invented to create user accounts).