message: Add a comment to `contains_proof` method.
diff: @@ -726,6 +726,7 @@ impl Block {
  self.proofs.push(proof)
  }
  + /// Returns true if block already contains the proof.
  pub(crate) fn contains_proof(&self, proof: &Signature) -> bool {
  self.proofs.iter().any(|s| s == proof)
  }
  