Add missing license headers.

PiperOrigin-RevId: 321069308
diff --git a/pom.xml b/pom.xml
index c95d8a8..5ae7a42 100644
--- a/pom.xml
+++ b/pom.xml
@@ -1,4 +1,20 @@
 <?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Copyright 2020 Google Inc.
+
+  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.
+-->
+
 <project
   xmlns="http://maven.apache.org/POM/4.0.0"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"