Update example to match against Option<String> returned by readline

src/bin/example.rs

 extern crate rustyline;
 
 fn main() {
-    rustyline::readline();
+    let readline = rustyline::readline();
+    match readline {
+        Some(line) => println!("Line: {:?}",line),
+        None       => println!("No input"),
+    }
 }