:memo: Clean-up `README.md`

[rneswold]

We should make sure the README.md reflects the purpose of this repo.

• Stress that it only consists of .proto files
• Remove any instructions on adding language-specific assets to the repo
• Add sections on how to use this repo with other languages' build environments

[rneswold]

With the new direction of this repo, we still need to update the README.md. But this time we should describe the layout and in which areas developers can create workflows and announce the "contract" we have in not breaking other languages' ability to use the protocols (due to a failing workflow, for instance.)