message: Add copyright headers to hello_world.star
diff: +# Copyright 2018 The Starlark in Rust Authors.
  +# Copyright (c) Facebook, Inc. and its affiliates.
  +#
  +# 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
  +#
  +# https://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.
  +
  # A simple Starlark file, as a Hello World
  def main():
  