message: Added missing license header in build-version.py
diff: #!/usr/bin/env python3
  +# Copyright 2020-2021 The Verible 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.
  """
  Invoke bazel with --workspace_status_command=bazel/build-version.py to
  get this invoked and populate bazel-out/volatile-status.txt
  