make echo server compile

The original code failed to compile with "expected item after doc comment" error message

README.md

@@ -8,8 +8,9 @@ use std::thread::spawn;
 use tungstenite::server::accept;
 
 /// A WebSocket echo server
-let server = TcpListener::bind("127.0.0.1:9001").unwrap();
-for stream in server.incoming() {
+fn main () {
+    let server = TcpListener::bind("127.0.0.1:9001").unwrap();
+    for stream in server.incoming() {
         spawn (move || {
             let mut websocket = accept(stream.unwrap()).unwrap();
             loop {
@@ -21,6 +22,7 @@ for stream in server.incoming() {
                 }
             }
         });
+    }
 }
 ```