input: Write a function to create a program that takes in a positive integer and uses a while loop to output the numbers counting down to 1. The function should print a message "Done!" after the loop ends.
  def count_down_to_one(num):
      while num > 0:
          print(num)
          num -= 1
      print("Done!")
  
  assert count_down_to_one(6)==None
  assert count_down_to_one(3)==None
  assert count_down_to_one(1)==None
output: def count_down_to_one(num):
      while num > 0:
          print(num)
          num -= 1
      print("Done!")