Data download script

[shanemcq18]

Data files used in the examples live on the data branch. We should have a script in the docs/ folder that downloads the data and puts it in the correct place so that the tutorials can be executed locally. This will also enable testing the documentation compilation through GitHub Actions (we had an action previously but it would pass even if a notebook cell failed to execute).

TODO:

• Write the script
• Update contributor guidelines
• Remove .pre-commit.yaml from the data branch?
• Reinstate GitHub Action for checking that the documentation compiles (there is also a LaTeX issue with plot labels, fix this too)

[shanemcq18]

.pre-commit.yaml removed from data branch in 463a19c.