Required free argument error is not very helpful

[Jordi Polo]

With a struct like

#[derive(Debug, Options)]
pub(crate) struct RawConfig {
    #[options(free, required, help = "File to run")]
    pub file_to_run: String,
    ....
    }

When run without any free parameters I get:
missing required free argument

Where I'd hope to get something like missing required argument file_to_run or such. I think users of this application will not understand what the free argument means, probably will try to call with a --free option or something.