make echo server compile

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

README.md

@@ -8,6 +8,7 @@ use std::thread::spawn;
 use tungstenite::server::accept;
 
 /// A WebSocket echo server
+fn main () {
     let server = TcpListener::bind("127.0.0.1:9001").unwrap();
     for stream in server.incoming() {
         spawn (move || {
@@ -22,6 +23,7 @@ for stream in server.incoming() {
             }
         });
     }
+}
 ```
 
 Take a look at the examples section to see how to write a simple client/server.