message: Add missing doc
diff: @@ -242,7 +242,7 @@ where
  Ok((era_supervisor, effects))
  }
  - // TODO[RC]: Add docs
  + /// Returns the merkle tree hash activation from the chainspec.
  pub(crate) fn merkle_tree_hash_activation(&self) -> EraId {
  self.chainspec.protocol_config.merkle_tree_hash_activation
  }
  