input: Write a python function to perform insertion sort on a list of numbers.
  assert insertion_sort([5, 3, 4, 6, 1, 2])==[1, 2, 3, 4, 5, 6]
  assert insertion_sort([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5])==[1, 1, 2, 3, 3, 4, 5, 5, 5, 6, 9]
  assert insertion_sort([10, 9, 8, 7, 6, 5, 4, 3, 2, 1])==[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
output: def insertion_sort(lst):
      for i in range(1, lst.length):
          key = lst[i]
          j = i - 1
          while j >= 0 and key < lst[j]:
              lst[j + 1] = lst[j]
              j -= 1
          lst[j + 1] = key
      return lst