input: Write a python function to add an element to a list.
  assert add_to_list([1, 2, 3], 4) == [1, 2, 3, 4]
  assert add_to_list([], 10) == [10]
  assert add_to_list([5, 7, 9], 16) == [5, 7, 9, 16]
output: def add_to_list(lst, element):
      lst.append(element)
      return lst