input: Write a function double_add that takes two integers num1 and num2 as input and returns the result of adding them together and then doubling the result.
  
  assert double_add(2, 3) == 10
  assert double_add(5, 7) == 24
  assert double_add(-1, 1) == 0
  assert double_add(0, 0) == 0
output: def double_add(num1, num2):
      return (num1 + num2) * 2