docs: update custom TLS certificate usage patch

[7-zete-7]

This will allow you to configure a custom certificate and not get the following error:

Error: adapting config using caddyfile: server listening on [:80] is HTTP, but attempts to configure TLS connection policies

This issue was mentioned in:

• https://github.com/dunglas/symfony-docker/discussions/359
• https://github.com/dunglas/symfony-docker/discussions/579
• https://github.com/dunglas/symfony-docker/issues/604
• https://github.com/dunglas/symfony-docker/pull/738

With this configuration, Caddy will use the configured certificate only for access via a secure protocol.