Footers are missing

[brian-rose]

Same as ProjectPythia/projectpythia.github.io#530, the shared footers are currently missing.

We can either add them directly to the myst.yml in this repo as in ProjectPythia/projectpythia.github.io#531, or fix the upstream config.

I'm going to start tagging things that should be resolved to coincide with our JOSE manuscript submission, this is one of them.