NF: Add Jupyter notebook widget for WebGL viewer

.github/workflows/build_docs.yml

@@ -34,12 +34,12 @@ jobs:
     - name: Install dependencies
       run: |
         sudo apt-get update
-        sudo apt-get install -y inkscape --no-install-recommends
+        sudo apt-get install -y inkscape pandoc --no-install-recommends
         pip install --upgrade pip
         pip install wheel setuptools numpy cython
         # force using latest nibabel
         pip install -U nibabel
-        pip install -q ipython Sphinx sphinx-gallery numpydoc # TODO: move to pyproject.toml
+        pip install -q ipython Sphinx sphinx-gallery numpydoc nbsphinx ipykernel # TODO: move to pyproject.toml
         pip install -e . --no-build-isolation --group dev
         python -c 'import cortex; print(cortex.__full_version__)'