Log error, if certificate is not found (#598)

Close #78

Author: umbynos

main.go

@@ -369,6 +369,7 @@ func loop() {
 	go func() {
 		// check if certificates exist; if not, use plain http
 		if _, err := os.Stat(filepath.Join(dest, "cert.pem")); os.IsNotExist(err) {
+			log.Error("Could not find HTTPS certificate. Using plain HTTP only.")
 			return
 		}