Consider using a github actions to automatically deploy the site

[ccamara]

Currently, the site needs to be deployed locally running ghp-import -n -p -f _build/html

This is fast and easy, but may cause divergences if something gets committed to main but the command for building the book is not run. Github actions could address that.

This page explains how to do it: https://jupyterbook.org/en/stable/publish/gh-pages.html

[ccamara]

Commit e23df4c is an attempt to do it. Regretfully, it fails because of this line: https://github.com/WarwickCIM/IM939_handbook/blob/e23df4c0f603be98287281e81ea374d46c81ebc1/.github/workflows/book.yml#L24

which calls requirements.txt which was deleted in favour of using a conda environment.

The default github action should be updated to include conda environments instead.