message: Add postscript explaining that --summary is default behaviour.
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"))]
  +#[structopt(group = ArgGroup::with_name("format_choice"), after_help = "If no output option is specified it defaults to --summary.")]
  pub struct Cli {
  // Format choice, optional:
  /// Optional argument for specifying the name of the format
  