Read the docs UI

I quite like the readthedocs UI--both the left side for chapters and right side for current content toc. Want to study this a bit and see how it scales on larger screens, etc.

https://jupyter-accessibility.readthedocs.io/

<img width="1467" alt="image" src="https://github.com/makeabilitylab/physcomp/assets/1621749/48e1bca7-d80b-4c6e-917d-3de2f1af3114">
