input: Write a python function to sort a list in descending order.
  assert sort_descending([3, 7, 2, 8, 10]) == [10, 8, 7, 3, 2]
  assert sort_descending([1, 5, 3, 9, 4]) == [9, 5, 4, 3, 1]
  assert sort_descending([10, 20, 15, 5, 30]) == [30, 20, 15, 10, 5]
output: def sort_descending(lst):
      return sorted(lst, reverse=True)