cfeat: adds extra credit details

Signed-off-by: Anthony D. Mays <[email protected]>

Author: anthonydmays

lesson_12/README.md

@@ -12,4 +12,8 @@ Please review the following resources before lecture:
 - [ ] Implement the `gameResult` method in [Lesson12.java](./structs_java/structs_app/src/main/java/com/codedifferently/lesson12/Lesson12.java).
 - [ ] Implement the `Stack` methods in [Stack.java](./structs_java/structs_app/src/main/java/com/codedifferently/lesson12/Stack.java).
 - [ ] Submit solutions via PR.
-- [ ] Do pre-work for [lesson 13](/lesson_13/).
+- [ ] Do pre-work for [lesson 13](/lesson_13/).
+
+### Extra credit
+
+- [ ] Complete TypeScript versions of methods in [lesson11.ts](./structs_ts/src/lesson12.ts) and [stack.ts](./structs_ts/src/stack.ts).