Update GPU install docs

website/_harp.json

@@ -66,8 +66,7 @@
                 { "id": 3, "title": "3.x", "checked": true }]
             },
             { "id": "config", "title": "Configuration", "multiple": true, "options": [
-                {"id": "venv", "title": "virtualenv", "help": "Use a virtual environment and install spaCy into a user directory" },
-                {"id": "gpu", "title": "GPU", "help": "Run spaCy on GPU to make it faster. Requires an NVDIA graphics card with CUDA 2+. See section below for more info."}]
+                {"id": "venv", "title": "virtualenv", "help": "Use a virtual environment and install spaCy into a user directory" }]
             },
             { "id": "model", "title": "Models", "multiple": true }
         ],

website/usage/_install/_instructions.jade

@@ -79,6 +79,13 @@ p
     python -m spacy validate
 
 +h(3, "gpu") Run spaCy with GPU
+    +tag experimental
+
++infobox("Important note", "⚠️")
+    |  The instructions below refer to installation with CUDA 8.0. In order to
+    |  install with CUDA 9.0, set the environment variable #[code CUDA9=1]
+    |  before installing Thinc. You'll also need to adjust the path to the
+    |  CUDA runtime.
 
 p
     |  As of v2.0, spaCy's comes with neural network models that are implemented
@@ -93,11 +100,11 @@ p
     |  CUDA. Finally, install spaCy.
 
 +code(false, "bash").
-    export CUDA_HOME=/usr/local/cuda-8.0 # Or wherever your CUDA is
+    export CUDA_HOME=/usr/local/cuda-8.0  # or wherever your CUDA is
     export PATH=$PATH:$CUDA_HOME/bin
 
     pip install spacy
-    python -c "import thinc.neural.gpu_ops" # Check the GPU ops were built
+    python -c "import thinc.neural.gpu_ops"  # check the GPU ops were built
 
 +h(3, "source") Compile from source
 

website/usage/_install/_quickstart.jade

@@ -11,9 +11,6 @@
     +qs({config: 'venv', os: 'linux'}) source .env/bin/activate
     +qs({config: 'venv', os: 'windows'}) .env\Scripts\activate
 
-    +qs({config: 'gpu', os: 'mac'}) export PATH=$PATH:/usr/local/cuda-8.0/bin
-    +qs({config: 'gpu', os: 'linux'}) export PATH=$PATH:/usr/local/cuda-8.0/bin
-
     +qs({package: 'pip'}) pip install -U spacy
     +qs({package: 'conda'}) conda install -c conda-forge spacy