Document how to trigger the native file dialog in derive and builder modes

[starthal]

Thanks for this crate!

It isn't clear (to me) from the documentation how to tell Klask to use a native dialog for a PathBuf argument.

I noticed the following:

use std::path::PathBuf;
use clap::{Arg, App, ValueHint};
use klask::Settings;

fn main() {
    // Displays path picker
    let app = App::new("Foo").arg(Arg::new("path").value_hint(ValueHint::FilePath));
    klask::run_app(app, Settings::default(), |matches| println!("Path: {:?}", matches.get_one::<PathBuf>("path")))
}
    
fn main() {
    // Displays string field
    #[derive(clap::Parser)]
    struct Args {
        path: PathBuf
    }
    klask::run_derived::<Args, _>(Settings::default(), |args| println!("Path: {:?}", args.path))
}

Is it possible to trigger the native dialog without supplying a ValueHint directly? If so, this could be helpful to note in the docs.

[starthal]

I just realized the Arg in the first snippet also needs .value_parser(value_parser!(PathBuf)) to work correctly.