examples: update hello world comment
-//! Hello world server.
-//!
//! A simple client that opens a TCP stream, writes "hello world\n", and closes
//! the connection.
//!
-//! You can test this out by running:
+//! To start a server that this client can talk to on port 6142, you can use this command:
//!
//! ncat -l 6142
//!
