code: def make_tarball(self, app_folder, build_data):
          
          # slugignore
          clean_slug_dir(app_folder)
  
          # tar up the result
          with tarfile.open('build.tar.gz', 'w:gz') as tar:
              tar.add(app_folder, arcname='')
          build_data.build_md5 = file_md5('build.tar.gz')
  
          tardest = os.path.join(self.outfolder, 'build.tar.gz')
          shutil.move('build.tar.gz', tardest)
  
          build_data_path = os.path.join(self.outfolder, 'build_result.yaml')
          print("Writing", build_data_path)
          with open(build_data_path, 'w') as f:
              f.write(build_data.as_yaml())
docs: Following a successful build, create a tarball and build result.