Create symbolic link to tails file named tails_hash for rev reg id rr_id.

        :param rr_id: rev reg id
        :param tails_hash: hash of tails file, serving as file name

def associate(base_dir: str, rr_id: str, tails_hash: str) -> None:
        """
        Create symbolic link to tails file named tails_hash for rev reg id rr_id.

        :param rr_id: rev reg id
        :param tails_hash: hash of tails file, serving as file name
        """

        cd_id = rev_reg_id2cred_def_id(rr_id)
        directory = join(base_dir, cd_id)
        cwd = getcwd()
        makedirs(directory, exist_ok=True)
        chdir(directory)
        symlink(tails_hash, rr_id)
        chdir(cwd)