message: Add note why Checksum::to_hex does not take a reference.
diff: @@ -18,7 +18,9 @@ impl Checksum {
  Checksum(Sha256::digest(wasm).into())
  }
  - /// Creates a lowercase hex encoded copy of this checksum
  + /// Creates a lowercase hex encoded copy of this checksum.
  + ///
  + /// This takes an owned `self` instead of a reference because `Checksum` is cheap to `Copy`.
  pub fn to_hex(self) -> String {
  self.to_string()
  }
  