Add extra details on using business cat for deployment

[xmedr]

Overview

This references our deploy-a-site docs in order to include instructions on adding Business Cat as a collaborator when deploying a Netlify app, and adds some context as to why we're using it.

• Closes #364

Testing Instructions

• Confirm whether those docs and added details help

[hancush]

This looks great, @xmedr – thanks for prompting me to dig this bit of rationale out of the archives, as it remains relevant today!