message: add textual markup
diff: @@ -63,7 +63,9 @@ pub fn encrypt<R: RngCore + CryptoRng>(
  /// Decrypt data in the asymmetric lock. this is the dual of 'encrypt'.
  /// The data should in the form:
  ///
  +/// ```text
  /// EPHEMERAL_PUBLIC_KEY || ENCRYPTED-DATA || POLY1305-TAG
  +/// ```
  ///
  /// # Return
  ///
  