-/// impl MaybeReadableArgs<u64> for YourCustomMessage {
-/// fn read<R: io::Read>(r: &mut R, message_type: u64) -> Result<Option<Self>, DecodeError> {
-/// # unreachable!()
-/// // Read your custom onion message of type `message_type` from `r`, or return `None`
-/// // if the message type is unknown
-/// }
-/// }