Merge pull request #733 from apogeeoak/intro

feat(intro): Proposal to add successfully compiling exercise as the first exercise.

exercises/variables/variables1.rs

@@ -1,10 +1,6 @@
 // variables1.rs
-// Make me compile! Execute the command `rustlings hint variables1` if you want a hint :)
-
-// About this `I AM NOT DONE` thing:
-// We sometimes encourage you to keep trying things on a given exercise,
-// even 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.
+// Make me compile!
+// Execute the command `rustlings hint variables1` if you want a hint :)
 
 // I AM NOT DONE