Minor improvements

docs/using/recipe_code/spellcheck_notebook_v6.dockerfile

@@ -0,0 +1,9 @@
+# Using Docker Hub here, because this image is old and not pushed to Quay.io
+FROM docker.io/jupyter/base-notebook:notebook-6.5.4
+
+RUN pip install --no-cache-dir 'jupyter_contrib_nbextensions' && \
+    jupyter contrib nbextension install --user && \
+    # can modify or enable additional extensions here
+    jupyter nbclassic-extension enable spellchecker/main --user && \
+    fix-permissions "${CONDA_DIR}" && \
+    fix-permissions "/home/${NB_USER}"