**Add Autocert details to the automatic domain registration doc** _Follow-up to [#1726](https://github.com/pomerium/documentation/pull/1726)_ What's incorrect or missing? - Little guidance on using Autocert for auto domain registration - Users may not realize Pomerium supports that flow What's the resolution? - Add step-by-step instructions for Autocert (setup, environment variables, domain prerequisites) - Link from "Certificates & TLS" or "Deploy" as needed