docs: update deployment guide

[ojeytonwilliams]

Checklist:

• [x] I have read freeCodeCamp's contribution guidelines.
• [x] My pull request has a descriptive title (not a vague title like Update index.md)

Closes https://github.com/freeCodeCamp/publish/issues/92

I think this is good enough for now, though we'll need to continue to update it as the deployment gets refined.