message: Update README.md with tf-nightly-gpu
diff: @@ -38,10 +38,11 @@ People who are a little more adventurous can also try our nightly binaries:
  **Nightly pip packages**
  * We are pleased to announce that TensorFlow now offers nightly pip packages
  -under the [tf-nightly](https://pypi.python.org/pypi/tf-nightly) project on pypi.
  -Simply run `pip install tf-nightly` in a clean environment to install the nightly
  -tensorflow build. We currently only support CPU packages on Linux, Mac, and Windows.
  -GPU packages on all platforms will arrive soon!
  +under the [tf-nightly](https://pypi.python.org/pypi/tf-nightly) and
  +[tf-nightly-gpu](https://pypi.python.org/pypi/tf-nightly-gpu) project on pypi.
  +Simply run `pip install tf-nightly` or `pip install tf-nightly-gpu` in a clean
  +environment to install the nightly TensorFlow build. We support CPU and GPU
  +packages on Linux, Mac, and Windows.
  **Individual whl files**
  