message: Improve comments for add_deploy and add_transfer
diff: @@ -63,6 +63,9 @@ impl AppendableBlock {
  /// Attempts to add a transfer to the block; returns an error if that would violate a validity
  /// condition.
  + ///
  + /// This _must_ be called with a transfer - the function cannot check whether the argument is
  + /// actually a transfer.
  pub(crate) fn add_transfer(
  &mut self,
  hash: DeployHash,
  @@ -87,6 +90,9 @@ impl AppendableBlock {
  /// Attempts to add a deploy to the block; returns an error if that would violate a validity
  /// condition.
  + ///
  + /// This _must not_ be called with a transfer - the function cannot check whether the argument
  + /// is actually not a transfer.
  pub(crate) fn add_deploy(
  &mut self,
  hash: DeployHash,
  