Update `centos-art.sh' script:
    
        - Initialize DOMAINNAME and MAILINGLIST variables. These variables
          let people to download the `centos-art.sh' script and adapt it
          to their own needs.
          
          The value of these variables must not be modified in the
          `centos-art.sh' script itself because it contains the
          information related to The CentOS Project. Instead, create a
          copy of `centos.art.sh' with a different name and set the
          information that describes your project there.
    
          The idea is let you reuse all the functionalities already
          available for `centos-art.sh' script and let you introduce new
          functionalities that you might need.