input: Write a python function to perform a linear search on a list of integers.
  assert LinearSearch([1, 2, 3, 4, 5], 3) == 2
  assert LinearSearch([10, 20, 30, 40, 50], 20) == 1
  assert LinearSearch([7, 14, 21, 28], 10) == -1
output: def LinearSearch(arr, target):
      for i in range(len(arr)):
          if arr[i] == target:
              return i
      return -1