added pidfile option to help message

src/desk-main.cpp

@@ -18,7 +18,8 @@ using namespace std;
 using namespace desk;
 
 void print_help(void){
-	cout << "\t-c / --config <config_file>  : config file" << endl;
+	cout << "\t-c / --config <config_file>  : config file (default: /etc/desk.conf)" << endl;
+	cout << "\t-p / --pidfile <pid_file>    : pid file    (default: /var/run/desk.pid)" << endl;
 	cout << "\t-d / --daemon                : daemonize" << endl;
 	cout << "\t-h / --help                  : print help" << endl;
 }