message: Print the default rage-mount help to stdout with no args or flags
diff: @@ -126,8 +126,22 @@ where
  }
  fn main() -> Result<(), Error> {
  + use std::env::args;
  +
  env_logger::builder().format_timestamp(None).init();
  + let args = args().collect::<Vec<_>>();
  +
  + if console::user_attended() && args.len() == 1 {
  + // If gumdrop ever merges that PR, that can be used here
  + // instead.
  + println!("Usage: {} [OPTIONS]", args[0]);
  + println!();
  + println!("{}", AgeMountOptions::usage());
  +
  + return Ok(());
  + }
  +
  let opts = AgeMountOptions::parse_args_default_or_exit();
  if opts.filename.is_empty() {
  