add Pandoc for notebook rendering

.github/workflows/generate_documentation.yml

@@ -30,6 +30,8 @@ jobs:
     - name: Install Sphinx and additional dependences
       run: |
         pip install sphinx sphinx-rtd-theme sphinx-autodoc-typehints sphinx-argparse nbsphinx renku-sphinx-theme
+    - name: Install Pandoc
+      uses: pandoc/actions/setup@{main}
     - name: Generate Documentation
       run: |
         cd docs_source