code: def add_resource(self, filename, env_filename):
      
      self._ensure_unfrozen('Adding a resource')
      self._copy_or_link(filename, env_filename, "resource")
docs: Add a resource to the PEX environment.
  
      :param filename: The source filename to add to the PEX; None to create an empty file at
        `env_filename`.
      :param env_filename: The destination filename in the PEX.  This path
        must be a relative path.