Make sure notebook is pip installed when building docs

CONTRIBUTING.rst

@@ -171,19 +171,17 @@ Building the Documentation
 To build the documentation you'll need `Sphinx <http://www.sphinx-doc.org/>`_,
 `pandoc <http://pandoc.org/>`_ and a few other packages.
 
-To install (and activate) a `conda environment`_ named ``notebook_docs``
+To install (and activate) a conda environment named ``notebook_docs``
 containing all the necessary packages (except pandoc), use::
 
-    conda env create -f docs/environment.yml
+    conda create -n notebook_docs pip
     conda activate notebook_docs  # Linux and OS X
-    activate notebook_docs         # Windows
-
-.. _conda environment:
-    https://conda.io/docs/user-guide/tasks/manage-environments.html#creating-an-environment-from-an-environment-yml-file
+    activate notebook_docs        # Windows
+    pip install .[docs]
 
 If you want to install the necessary packages with ``pip``, use the following instead::
 
-    pip install -r docs/doc-requirements.txt
+    pip install .[docs]
 
 Once you have installed the required packages, you can build the docs with::