input: Write a function to create a Python program that takes in a positive integer, then uses a while loop to output the numbers counting down to 1. The function should print each number and finally print "Done!".
  def count_down(num):
      while num > 0:
          print(num)
          num -= 1
      print("Done!")
  
  assert count_down(6) == None
  assert count_down(3) == None
  assert count_down(1) == None
output: def count_down(num):
      while num > 0:
          print(num)
          num -= 1
      print("Done!")