Collapsible Code Blocks for Training Logs

[nelson-liu]

We're planning on putting training logs of various models in doc/models/about_models.rst, but they're quite long which reduces readability. It'd be nice to have these blocks collapsed by default, but I think this is a feature request for the readthedocs sphinx theme.

Alternatively, we could manually add the theme as a submodule to this repo in our doc folder (wherever sphinx looks for themes), remove the theme from the conf.py and requirements.txt, then build the docs with our locally changed version.