Document use of process.stderr.write() vs console.error()

In this repo, `process.stderr.write(util.inspect(arg) + '\n')` is preferred over `console.error(arg)`.

Per https://github.com/getodk/central-backend/pull/1414#issuecomment-2669993120, there are reasons `process.stderr.write(util.inspect(arg) + '\n')` is used, but they are not known.

It would be helpful to have this reasoning documented somewhere, as it would seem more idiomatic to use `console.error(arg)`.