input: For example,
  >>> insertion_sort([4, 2, 7, 1, 3])
  [1, 2, 3, 4, 7]
  >>> insertion_sort([10, 5, 8, 1, 32, 7])
  [1, 5, 7, 8, 10, 32]
output:     
      for i in range(1, len(arr)):
          key = arr[i]
          j = i - 1
          while j >= 0 and key < arr[j]:
              arr[j + 1] = arr[j]
              j -= 1
          arr[j + 1] = key
      return arr
  