code: func detectCryptoBackend(ctx context.Context, path string) backend.CryptoBackend {
  	if fsutil.IsFile(filepath.Join(path, xc.IDFile)) {
  		return backend.XC
  	}
  	return backend.GPGCLI
  }
docs: // detectCryptoBackend tries to detect the crypto backend used in a cloned repo
  // This detection is very shallow and doesn't support all backends, yet
  // TODO(dschulz) must not depend on xc, move to registry