Figure out if there's a way to tag all cells to be hidden

[TeaganKing]

Currently, as far as I'm aware, users need to tag each cell as hidden in order to prevent code from showing up in the Jupyter book. Although this method technically works, it'd be nice to have (or find and document) a 'select all' method to tag most of the cells in a notebook to be hidden.

[TeaganKing]

See #60 for explanation for hiding individual cells

[kafitzgerald]

It looks like this (link below) might be an option for adding tags programmatically, but haven't used nbformat before and don't have a great feel for how you might want to integrate this.

https://jupyterbook.org/en/stable/content/metadata.html#add-tags-using-python-code