specfile: %license field is now used for the license file
    
      Rename 'Copyright' to 'COPYING', as it is more common name nowadays.
      The 'COPYING' file will be installed into /usr/share/licenses/tcsh
      folder, to comply with the Fedora Packaging/Licensing guidelines:
      https://fedoraproject.org/wiki/Packaging:LicensingGuidelines#License_Text