add head for warmupTrigger

Author: kaibocai

src/main/java/com/microsoft/azure/functions/annotation/WarmupTrigger.java

@@ -1,3 +1,9 @@
+/**
+ * Copyright (c) Microsoft Corporation. All rights reserved.
+ * Licensed under the MIT License. See License.txt in the project root for
+ * license information.
+ */
+
 package com.microsoft.azure.functions.annotation;
 
 import java.lang.annotation.ElementType;