net: add set_nonblocking to doc (#3100)

tokio/src/net/tcp/listener.rs

@@ -218,6 +218,7 @@ impl TcpListener {
     /// #[tokio::main]
     /// async fn main() -> Result<(), Box<dyn Error>> {
     ///     let std_listener = std::net::TcpListener::bind("127.0.0.1:0")?;
+    ///     std_listener.set_nonblocking(true)?;
     ///     let listener = TcpListener::from_std(std_listener)?;
     ///     Ok(())
     /// }

tokio/src/net/tcp/stream.rs

@@ -159,6 +159,7 @@ impl TcpStream {
     /// #[tokio::main]
     /// async fn main() -> Result<(), Box<dyn Error>> {
     ///     let std_stream = std::net::TcpStream::connect("127.0.0.1:34254")?;
+    ///     std_stream.set_nonblocking(true)?;
     ///     let stream = TcpStream::from_std(std_stream)?;
     ///     Ok(())
     /// }

tokio/src/net/udp/socket.rs

@@ -187,6 +187,7 @@ impl UdpSocket {
     /// # async fn main() -> io::Result<()> {
     /// let addr = "0.0.0.0:8080".parse::<SocketAddr>().unwrap();
     /// let std_sock = std::net::UdpSocket::bind(addr)?;
+    /// std_sock.set_nonblocking(true)?;
     /// let sock = UdpSocket::from_std(std_sock)?;
     /// // use `sock`
     /// # Ok(())

tokio/src/net/unix/datagram/socket.rs

@@ -179,6 +179,7 @@ impl UnixDatagram {
     /// // Bind the socket to a filesystem path
     /// let socket_path = tmp.path().join("socket");
     /// let std_socket = StdUDS::bind(&socket_path)?;
+    /// std_socket.set_nonblocking(true)?;
     /// let tokio_socket = UnixDatagram::from_std(std_socket)?;
     ///
     /// # Ok(())