update sample config

goguerrilla.conf.sample

@@ -10,7 +10,10 @@
     ],
     "pid_file" : "/var/run/go-guerrilla.pid",
     "backend_config": {
-        "log_received_mails": true
+        "log_received_mails": true,
+        "save_workers_size": 1,
+        "process_stack" : "HeadersParser|Header|Debugger",
+        "primary_mail_host" : "mail.example.com"
     },
     "servers" : [
         {