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