Function discover 

pub async fn discover<T, D>(directories: D) -> Vec<T>
where
    T: ConfigFile,
    D: IntoIterator + Send + 'static,
    D::Item: AsRef<Path>,

Discovers config files in the given directories.

If multiple config files have the same identifier, the one that is discovered first is kept. It is guaranteed that earlier directories have higher priority, but it’s undefined which file is kept if multiple files share the same identifier in the same directory.

The config files are sorted by their identifier (ascending).