fix: re-add missing done comments

exercises/clippy/clippy3.rs

@@ -1,6 +1,8 @@
 // clippy3.rs
 // Here's a couple more easy Clippy fixes, so you can see its utility.
 
+// I AM NOT DONE
+
 #[allow(unused_variables, unused_assignments)]
 fn main() {
     let my_option: Option<()> = None;