add missing header (#42)

Author: dbraquart

src/main/java/org/gridsuite/notification/server/NotificationServerRuntimeException.java

@@ -1,3 +1,10 @@
+/**
+ * Copyright (c) 2022, RTE (http://www.rte-france.com)
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
 package org.gridsuite.notification.server;
 
 public class NotificationServerRuntimeException extends RuntimeException {