Simplify website development workflow

Right now, the website development workflow requires one to use `docker` (see site/README.md).

Since we use `bundler` as a level of abstraction already, we could consider removing `docker` as an abstraction on top.

Things to figure out: How to get non-bundler-managed dependencies (e.g., ruby, ruby-devel, doxygen) installed in a platform agnostic way.

Another option to simplify would be to still use `docker`, but consolidate the website development workflow with the website publishing workflow.