Resolve "Create engineering docs in project"

1. Change Summary

1. Adds /docs/ directory with initial iteration of project engineering documentation
2. Adds (eventual) live link to the docs directory to our project's MR template and README

Markdown preview link: https://gitlab.com/gitlab-com/marketing/digital-experience/about-gitlab-com/-/tree/f24ead1abd3bda7bc386864d46fd1cbc8e1f79e2/docs

Closes #24 (closed)