Documentation for use your own SSL certs conflicts with docs from nginx-proxy

https://jippi.github.io/docker-pixelfed/customize/faq/#how-do-i-use-my-own-ssl-certificate says to name them `${APP_DOMAIN}.cert.pem` and `${APP_DOMAIN}.key.pem` plus some chain files. However, the [docs for nginx-proxy](https://github.com/nginx-proxy/nginx-proxy/tree/main/docs#ssl-support) say:

> The contents of `/path/to/certs` should contain the certificates and private keys for any virtual hosts in use. The certificate and keys should be named after the virtual host with a `.crt` and `.key` extension. For example, a container with `VIRTUAL_HOST=foo.bar.com` should have a `foo.bar.com.crt` and `foo.bar.com.key` file in the certs directory.

I'm trying to use this for local development with a self-signed certificate. I had `ERR_SSL_UNRECOGNIZED_NAME_ALERT` with no option to accept the certificate anyway when I followed this project's docs. After switching my filenames to `localhost.crt` and `localhost.key` and ignoring the chain ones, the browser started receiving a certificate and just complaining about it being self-signed, giving me an option to bypass that.

I thought about sending a patch to change the docs, but I don't know how the LetsEncrypt part interacts and didn't want to break the docs related to those.

Relatedly, the healthchecks on this project fail if the certificate is self-signed. I had to add `-k` to the `curl` commands.

Start with the FAQ section at customize/faq/#how-do-i-use-my-own-ssl-certificate and compare its filenames with the nginx-proxy SSL support documentation. Check the healthcheck curl commands and verify the expected behavior for self-signed certificates; done means the certificate guidance is consistent without breaking the Let's Encrypt instructions, and healthchecks handle the documented local-development case.

Written by the indexing model from the issue text.