input: Write a python function to sort a list in descending order.
  assert sort_descending([4, 9, 2, 6, 5]) == [9, 6, 5, 4, 2]
  assert sort_descending([10, 3, 5, 8, 2]) == [10, 8, 5, 3, 2]
  assert sort_descending([1, 7, 3, 9, 0]) == [9, 7, 3, 1, 0]
output: def sort_descending(lst):
      return sorted(lst, reverse=True)