fix(arc1): Fix some words in the comment

exercises/standard_library_types/arc1.rs

@@ -1,8 +1,8 @@
 // arc1.rs
 // Make this code compile by filling in a value for `shared_numbers` where the
-// TODO comment is and creating an initial binding for `child_numbers`
+// TODO comment is and create an initial binding for `child_numbers`
 // somewhere. Try not to create any copies of the `numbers` Vec!
-// Execute `rustlings help arc1` for hints :)
+// Execute `rustlings hint arc1` for hints :)
 
 // I AM NOT DONE