input: Write a python function to compute the root mean squared displacement (RMSD) of two points after random walk steps.
  assert rmsd((0, 0), (3, 4)) == 5.0
  assert rmsd((10, 10), (13, 14)) == 5.0
  assert rmsd((-3, -4), (0, 0)) == 5.0
output: def rmsd(point1, point2):
      return ((point2[0] - point1[0]) ** 2 + (point2[1] - point1[1]) ** 2) ** 0.5