Add documentation on how to fix build failures

[NeuroShepherd]

Currently, I'm allowing Quarto to build the .Rmd file in this repo during the GH Action to publish the site. However, the package dependencies also need to be installed during this process. If more dependencies are added at some point, the pipeline will break. Two options:

1. Explain how to install additional dependencies in publish.yml
2. Explain how to prevent the rendering of the .Rmd file since it is not strictly necessary at this time.

[NeuroShepherd]

Caching now uses setup-r-dependencies. Document this in the README as well as point 1 in the above comment.