update link to example

in my environment i see the matrix. conf in that file: /matrix/nginx-proxy/conf.d/matrix-domain.conf

docs/configuring-playbook-ssl-certificates.md

@@ -99,7 +99,7 @@ The certificate files would be made available in `/matrix/ssl/config/live/<your-
 
 For automated certificate renewal to work, each port `80` vhost for each domain you are obtaining certificates for needs to forward requests for `/.well-known/acme-challenge` to the certbot container we use for renewal.
 
-See how this is configured for the `matrix.` subdomain in `/matrix/nginx-proxy/conf.d/matrix-synapse.conf`
+See how this is configured for the `matrix.` subdomain in `/matrix/nginx-proxy/conf.d/matrix-domain.conf`
 Don't be alarmed if the above configuration file says port `8080`, instead of port `80`. It's due to port mapping due to our use of containers.