message: added comments to describe solution
diff: class Solution:
  def xorOperation(self, n: int, start: int) -> int:
  + # build the initial array of numbers following the formula
  nums = list()
  for i in range(n):
  nums.append(2 * i + start)
  + # compute the xor of all of the numbers
  xor = nums[0]
  for num in nums[1:]:
  xor ^= num
  