fix: move_semantics5 hints

Improve the hints for move_semantics5, as well as the explanatory
comments in the code.

Previously, it was not clear what possible changes were allowed.
It seems that reordering the statements might be the intended solution.
The previous comment about not "adding newlines" doesn't make sense,
so treating it as "adding new lines" makes it more clear.

exercises/move_semantics/move_semantics5.rs

@@ -1,5 +1,6 @@
 // move_semantics5.rs
-// Make me compile without adding any newlines or removing any of the lines.
+// Make me compile without adding, removing, or changing any of the
+// lines in `main()`.
 // Execute `rustlings hint move_semantics5` for hints :)
 
 // I AM NOT DONE