input: Write a python function to add two matrices element-wise.
  assert addMatrix([[1, 2], [3, 4]], [[5, 6], [7, 8]]) == [[6, 8], [10, 12]]
  assert addMatrix([[1, 0], [0, 1]], [[0, 1], [1, 0]]) == [[1, 1], [1, 1]]
  assert addMatrix([[2, 3], [4, 5]], [[1, 1], [1, 1]]) == [[3, 4], [5, 6]]
output: def addMatrix(matrix1, matrix2):
      return [[matrix1[i][j] + matrix2[i][j] for j in range(len(matrix1[0]))] for i in range(len(matrix1))]