input: Write a python function to compute the sum of a list of numbers.
  assert sum_list([1, 2, 3, 4, 5, 6]) == 21
  assert sum_list([10, 20, 30, 40]) == 100
  assert sum_list([0, -1, 1]) == 0
output: def sum_list(numbers):
      return sum(numbers)