Add -n flag

src/main.rs

@@ -124,6 +124,9 @@ async fn main() {
         let addr: SocketAddr = address.parse().unwrap();
         config.address = Some(addr);
     }
+    if let Some(servername) = matches.opt_str("n") {
+        config.servername = Some(servername);
+    }
 
     let addr = match config.address {
         Some(SocketAddr::V6(addr)) => addr.clone(),