input: Write a function named insertionSort that takes a list of integers as input and sorts it using the Insertion Sort algorithm. The function should return the sorted list.
  assert insertionSort([3, 2, 1])==[1, 2, 3]
  assert insertionSort([1])==[1]
  assert insertionSort([])==[]
  assert insertionSort([5, 3, 8, 4, 6])==[3, 4, 5, 6, 8]
output: def insertionSort(arr):
      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