message: Update README.md
  this is not a "pure python" implementation anymore
diff: Minigo: A minimalist Go engine modeled after AlphaGo Zero, built on MuGo
  ==================================================
  -This is a pure Python implementation of a neural-network based Go AI, using
  -TensorFlow. While inspired by DeepMind's AlphaGo algorithm, this project is not
  +This is an implementation of a neural-network based Go AI, using TensorFlow.
  +While inspired by DeepMind's AlphaGo algorithm, this project is not
  a DeepMind project nor is it affiliated with the official AlphaGo project.
  ### This is NOT an official version of AlphaGo ###
  