Update README.md + fixed taking square roots to avoid NANs

[brando90]

added

pip install -U git+https://github.com/google/svcca

to allow installations

[brando90]

important change so code does not returns nans:

  import scipy
  # print('npy\'s sqrt')
  invsqrt_xx = scipy.linalg.sqrtm(inv_xx)
  invsqrt_yy = scipy.linalg.sqrtm(inv_yy)

instead of

  # print('their sqrt')
  # invsqrt_xx = positivedef_matrix_sqrt(inv_xx)
  # invsqrt_yy = positivedef_matrix_sqrt(inv_yy)