The extension should notify the user to install Python and the Python extension when attempting to export a notebook if they are not installed

[xiaoxi-david]

Currently, the extension requires Python and the Python extension to export a Jupyter notebook. But, if you lack either, the drop-down menu asking for a Python environment is blank and VSCode gives you no information about what to do.

I would like the extension to notify the user to install Python and the Python extension when trying to export a notebook if they are not installed.