fix: Added comments on the function for clarity on coding-interview-prep (#42689)

curriculum/challenges/english/10-coding-interview-prep/data-structures/remove-items-from-a-set-in-es6.md

@@ -48,7 +48,10 @@ assert(
 
 ```js
 function checkSet(){
+  // Only change code below this line
   var set = null;
+
+  // Only change code above this line
   return set;   
 }
 ```