message: nydus-image: use sha256 as default digester
  Use sha256 as default digestor, it's commonly used to digest container
  images.
diff: @@ -255,7 +255,7 @@ fn prepare_cmd_args(bti_string: &'static str) -> App {
  .short('d')
  .help("algorithm to digest inodes and data chunks:")
  .required(false)
  - .default_value("blake3")
  + .default_value("sha256")
  .value_parser(["blake3", "sha256"]),
  )
  .arg(
  