s3s-fs: cli docs

use tracing::info;

#[derive(Debug, Parser)]

#[command(version)]

struct Opt {

    #[clap(long, default_value = "localhost")]

    /// Host name to listen on.

    #[arg(long, default_value = "localhost")]

    host: String,

    #[clap(long, default_value = "8014")]

    /// Port number to listen on.

    #[arg(long, default_value = "8014")] // The original design was finished on 2020-08-14.

    port: u16,

    #[clap(long, requires("secret-key"))]

    /// Access key used for authentication.

    #[arg(long, requires("secret-key"))]

    access_key: Option<String>,

    #[clap(long, requires("access-key"))]

    /// Secret key used for authentication.

    #[arg(long, requires("access-key"))]

    secret_key: Option<String>,

    #[clap(long)]

    /// Domain name used for virtual-hosted-style requests.

    #[arg(long)]

    domain_name: Option<String>,

    /// Root directory of stored data.

    root: PathBuf,

}