Add timer example

examples/timer.rs

@@ -0,0 +1,14 @@
+use std::time::{Duration, Instant};
+
+use smol::Timer;
+
+fn main() {
+    futures::executor::block_on(async {
+        let start = std::time::Instant::now();
+
+        let dur = Duration::from_secs(1);
+        Timer::after(dur).await;
+
+        dbg!(start.elapsed());
+    })
+}