Documentation for TLS certificates managed by Caddy

# Use case

I use Caddy to manage my certificates. [The documentation](https://foxcpp.dev/maddy/tutorials/setting-up/) mentions how to work with Let's Encrypt and certbot and ACME.sh, but I don't use those and don't know how to use those.

# Your idea for a solution

Could we please write some documentation on how to work with TLS certificates managed by Caddy? I'd be willing to help test the instructions as a clueless noob.

- [x] I'm willing to help with the implementation

Start with the linked setting-up tutorial and compare its Let's Encrypt, certbot, and ACME.sh guidance with Caddy-managed certificates. Verify the instructions using a Caddy-managed certificate, then document the setup and usage clearly enough for the reported use case.

Written by the indexing model from the issue text.