Add explanation comment for 4-random.js

Author: salahalsabhi

Sprint-2/1-key-exercises/4-random.js

@@ -8,3 +8,4 @@ console.log(num);
 // Try breaking down the expression and using documentation to explain what it means
 // It will help to think about the order in which expressions are evaluated
 // Try logging the value of num and running the program several times to build an idea of what the program is doing
+// num is a random whole number between 1 and 100