message: Slightly reword help text for format selections.
diff: @@ -7,15 +7,15 @@ use structopt::{clap::ArgGroup, StructOpt};
  #[derive(StructOpt, Debug)]
  #[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
  - /// example "opentype", that will be used to process the files.
  + // Format choice, optional:
  + /// Optional argument for specifying the name of the format
  + /// description in the installed catalog, for example "opentype",
  + /// that will be used to process the files.
  #[structopt(long, group = "format_choice")]
  format: Option<String>,
  - /// --format-file=FILE is an optional argument for specifying the
  - /// file containing the format description, for example
  - /// "path/to/myformat.ddl", that will be used to process the
  - /// files.
  + /// Optional argument for specifying the file containing the
  + /// format description, for example "path/to/myformat.ddl", that
  + /// will be used to process the files.
  #[structopt(long, group = "format_choice")]
  format_file: Option<PathBuf>,
  // The (binary) input files to operate on:
  