Add hints to the variable bindings exercises

variables/variables1.rs

@@ -1,6 +1,41 @@
-// Make me compile!
+// Make me compile! Scroll down for hints :)
 
 fn main() {
     x = 5;
     println!("x has the value {}", x);
 }
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+// Hint: The declaration on line 4 is missing a keyword that is needed in Rust
+// to create a new variable binding.