Document error message and explanation in 2.js

Added comments explaining the error and its correction.

Author: cywong-dev

Sprint-2/1-key-errors/2.js

@@ -11,10 +11,17 @@ function square(3) {
 
 // =============> write the error message here
 
+// [ChunYanWong] Uncaught SyntaxError SyntaxError: Unexpected number
+
 // =============> explain this error message here
 
+// [ChunYanWong] number 3 cannot be parameter
+
 // Finally, correct the code to fix the problem
 
 // =============> write your new code here
 
+// [ChunYanWong] function square(num) {
+// ...
+