message: Document pub enum Rseed<Fs> with link to ZIP 212
diff: @@ -223,6 +223,11 @@ impl<E: JubjubEngine> PaymentAddress<E> {
  }
  }
  +/// Enum for note randomness before and after [ZIP 212](https://zips.z.cash/zip-0212).
  +///
  +/// Before ZIP 212, the note commitment trapdoor `rcm` must be a scalar value.
  +/// After ZIP 212, the note randomness `rseed` is a 32-byte sequence, used to derive
  +/// both the note commitment trapdoor `rcm` and the ephemeral private key `esk`.
  #[derive(Copy, Clone, Debug)]
  pub enum Rseed<Fs> {
  BeforeZip212(Fs),
  