docs: def output_files(self):
          """Returns list of output files from this rule, relative to buildroot.
  
          In this case it's simple (for now) - the output files are enumerated in
          the rule definition.
          """
          outs = [os.path.join(self.address.repo, self.address.path, x)
                  for x in self.params['outs']]
          return outs