feat(intro1): add more hints

exercises/intro/intro1.rs

@@ -4,6 +4,10 @@
 // after you already figured it out. If you got everything working and feel
 // ready for the next exercise, remove the `I AM NOT DONE` comment below.
 // Execute the command `rustlings hint intro1` for a hint.
+//
+// If you're running this using `rustlings watch`: The exercise file will be reloaded
+// when you change one of the lines below! Try adding a `println!` line, or try changing
+// what it outputs in your terminal. Try removing a semicolon and see what happens!
 
 // I AM NOT DONE
 
@@ -20,4 +24,7 @@ fn main() {
     println!("This exercise compiles successfully. The remaining exercises contain a compiler");
     println!("or logic error. The central concept behind Rustlings is to fix these errors and");
     println!("solve the exercises. Good luck!");
+    println!();
+    println!("The source for this exercise is in `exercises/intro/intro1.rs`. Have a look!");
+    println!("Going forward, the source of the exercises will always be in the success/failure output.");
 }