add license headers to release-notes.sh script

Signed-off-by: Paul Czarkowski <username.taken@gmail.com>

scripts/release-notes.sh

@@ -1,4 +1,18 @@
-#!/bin/bash
+#!/usr/bin/env bash
+
+# Copyright The Helm Authors.
+#
+# 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.
 
 RELEASE=${RELEASE:-$2}
 PREVIOUS_RELEASE=${PREVIOUS_RELEASE:-$1}