Update PalindromeNumber.js

- Added link to the problem
- Added T.C. as well as S.C.

Author: 09xHarsh

javascript/PalindromeNumber.js

@@ -1,3 +1,7 @@
+// https://leetcode.com/problems/palindrome-number
+// T: O(log(n))
+// S: O(1)
+
 const isPalindrome = (x) => {
   if (x < 0 || (x % 10 === 0 && x !== 0)) {
     return false;