Add missing header

Author: AB-xdev

chartjs-java-model/src/main/java/software/xdev/chartjs/model/dataset/DoughnutDatasetBase.java

@@ -1,3 +1,18 @@
+/*
+ * Copyright © 2023 XDEV Software (https://xdev.software)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 package software.xdev.chartjs.model.dataset;
 
 /**