Add note about load-bearing '/en/' in PUBLIC_URL configuration

nix-system-configs/modules/system/traefik.nix

@@ -123,6 +123,7 @@ in {
             # When running Anubis in reverse-proxy (inline) mode we must tell
             # the instance the public URL it serves so redirects and assets use
             # the protected host instead of the central anubis host.
+            # NOTE: THE '/en/' is load bearing.
             PUBLIC_URL = "https://partdb.prg-radio.org/en/";
             DIFFICULTY = 20;
             SERVE_ROBOTS_TXT = true;