The super(String) invocation just calls the CommandGroup's constructor (which is a Command object itself) that takes a string parameter. This parameter sets the name to associate with the command. It is not required (the default constructor will) work.
Setting the name on the Command objects can sometimes be useful when debugging. For example, if you add the line after your shooter subsystem is created, the smart dashboard will display the command that is currently active on it:
Code:
SmartDashboard.putData("Shooter", Robot.shooter);