add copyright

Signed-off-by: Fabio Di Fabio <fabio.difabio@consensys.net>

ethereum/blockcreation/src/main/java/org/hyperledger/besu/ethereum/blockcreation/BlockCreationTiming.java

@@ -1,3 +1,17 @@
+/*
+ * Copyright Hyperledger Besu Contributors.
+ *
+ * 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.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
 package org.hyperledger.besu.ethereum.blockcreation;
 
 import java.time.Duration;