[doc] comments

src/main.rs

@@ -77,6 +77,7 @@ fn main() -> EmulatorResult<()> {
 
         canvas.present();
 
+        // 60fps - small offset to consider for cpu cycle time
         ::std::thread::sleep(Duration::new(0, 1_000_000_000u32 / 60 - 2000_000));
     }