Add logging to WhatsAppReminder

src/main/java/de/jeyp91/whatsapp/WhatsAppNotifier.java

@@ -33,6 +33,7 @@ public class WhatsAppNotifier {
             boolean success = sendMessage(reminder);
             if (success) {
                 markReminderAsSent(reminder);
+                logger.info("WhatsApp Erinnerung an " + reminder.username() + " gesendet.");
             }
         });
     }