update instructions append

exercises/practice/list-ops/.docs/instructions.append.md

@@ -2,8 +2,18 @@
 
 ## Appendix
 
-The instructions are synced with a shared repository to maintain consistency across all language tracks.
-For this exercise in the Clojure track, assume that both the input and output are vectors.
+The instructions are synced with a shared repository to ensure consistency across all language tracks.
+For this exercise in the Clojure track, assume both the input and output are vectors.
+As a stretch goal, consider how you could implement the solution without using lists anywhere in your code.
+Also, think about the efficiency of your program.
 
 It is important not to reuse existing Clojure built-in functions with similar functionality, as doing so would diminish the intended learning value of the exercise.
-Some of these functions include `into`, `concat`, `cat`, `lazy-cat`, `mapcat`, `flatten`, `filter`, `filterv`, `remove`, `count`, `map`, `mapv`, `reduce`, `transduce`, `reverse`, and `rseq`, all from the **clojure.core** namespace.
+Key functions from the **clojure.core** namespace to avoid include `into`, `concat`, `cat`, `lazy-cat`, `mapcat`, `flatten`, `filter`, `filterv`, `remove`, `count`, `map`, `mapv`, `reduce`, `transduce`, `reverse`, and `rseq`.
+
+### Optional goals
+
+Try to pass the tests by devising a solution that assumes both the input and output are lists instead of vectors.
+The test suite does not need to be modified.
+This time, consider how you could implement the solution without using vectors anywhere in your code.
+
+If you decide to publish this solution, be sure to include a comment indicating that it addresses the optional goal of using lists. Don't forget to update the docstrings!