docs(mioudp): move docs

Author: mkroening

examples/mioudp/src/main.rs

@@ -1,10 +1,10 @@
+//! Adapted from <https://github.com/tokio-rs/mio/blob/c9831c78d14fd54c41bab79f5347764a56dc8326/examples/udp_server.rs>.
+
 use std::io;
 use std::str::from_utf8;
 
 #[cfg(target_os = "hermit")]
 use hermit as _;
-// This example is derived from
-// https://github.com/tokio-rs/mio/blob/master/examples/tcp_server.rs
 use log::warn;
 use mio::{Events, Interest, Poll, Token};