message: Remove default setting, required=false.
diff: @@ -5,7 +5,7 @@ use structopt::{clap::ArgGroup, StructOpt};
  /// Fathom DDL interpreter to provide tools to inspect and query binary files.
  #[derive(StructOpt, Debug)]
  -#[structopt(group = ArgGroup::with_name("format_choice").required(false))]
  +#[structopt(group = ArgGroup::with_name("format_choice"))]
  pub struct Cli {
  /// --format=NAME is an optional argument for specifying the name
  /// of the format description in the installed catalog, for
  