ft: add version flag and some docs for format flag

cli/src/main.rs

···
 }
 
 #[derive(Debug, Parser)]
+#[command(version, about)]
 struct Args {
+    /// Output format type
     #[arg(long, default_value_t = fuk::output::Format::JSON)]
     format: fuk::output::Format,
     /// File containing list of keys to be fetched