[Docs] Add a note for TLS with localhost

[Pierstoval]

It's mostly a note for people that don't know Caddy's TLS system, as I stumbled upon this issue this morning, and forgot that Caddy's localhost vs 127.0.0.1 TLS handling is not the same 😅

[dunglas]

The certificate will never be trusted by default by the host anyway because the app runs in a container.

[Pierstoval]

Indeed, but by using localhost you get a browser warning telling you to "accept the risk", while when using IP addresses or other domain names you end up with an unrecoverable ssl error that prevents you from using the app altogether

[dunglas]

I suggest just adding and accept the self-signed certificate to the existing sentence in the readme. We can add a new doc entry about TLS if necessary but I would like to not "pollute" the readme too much.

[Pierstoval]

Done 👍