chore: add explanatory comment to clippy1

exercises/clippy/clippy1.rs

@@ -2,6 +2,8 @@
 // The Clippy tool is a collection of lints to analyze your code
 // so you can catch common mistakes and improve your Rust code.
 //
+// For these exercises the code will fail to compile when there are clippy warnings
+// check clippy's suggestions from the output to solve the exercise.
 // Execute `rustlings hint clippy1` for hints :)
 
 // I AM NOT DONE