[docs] Update RLlib install to not include Tensorflow (#2178)

doc/source/rllib.rst

@@ -31,15 +31,27 @@ including custom ones written and registered by the user.
 Installation
 ------------
 
-RLlib has extra dependencies on top of **ray**. You might also want to clone the Ray repo for convenient access to RLlib helper scripts:
+RLlib has extra dependencies on top of **ray**. First, you'll need into install either PyTorch or TensorFlow.
+For usage of PyTorch models, visit the `PyTorch website <http://pytorch.org/>`__
+for instructions on installing PyTorch.
+
+.. code-block:: bash
+
+  pip install tensorflow  # or tensorflow-gpu
+
+Then, install Ray with extra RLlib dependencies:
 
 .. code-block:: bash
 
   pip install 'ray[rllib]'
+
+You might also want to clone the Ray repo for convenient access to RLlib helper scripts:
+
+.. code-block:: bash
+
   git clone https://github.com/ray-project/ray
 
-For usage of PyTorch models, visit the `PyTorch website <http://pytorch.org/>`__
-for instructions on installing PyTorch.
+
 
 Getting Started
 ---------------

python/setup.py

@@ -64,11 +64,7 @@ else:
 
 optional_ray_files += ray_autoscaler_files
 
-extras = {
-    "rllib": [
-        "tensorflow", "pyyaml", "gym[atari]", "opencv-python", "lz4", "scipy"
-    ]
-}
+extras = {"rllib": ["pyyaml", "gym[atari]", "opencv-python", "lz4", "scipy"]}
 
 
 class build_ext(_build_ext.build_ext):