add copyright notice to tombstone.proto

Author: supervacuus

sentry-android-core/src/main/proto/io/sentry/android/core/internal/tombstone/tombstone.proto

@@ -2,6 +2,20 @@
 // Sentry changes:
 // * change the java_package
 //
+// Copyright (C) 2020 The Android Open Source Project
+//
+// 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.
+//
 // Protobuf definition for Android tombstones.
 //
 // An app can get hold of these for any `REASON_CRASH_NATIVE` instance of