add copyright and module docstring

proto/private/bzlmod_deps.bzl

@@ -1,3 +1,27 @@
+# Copyright 2022 The Bazel Authors. All rights reserved.
+#
+# 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.
+
+# Redefine native symbols with a new name as a workaround for
+# exporting them in `//proto:defs.bzl` with their original name.
+#
+# While we cannot force users to load these symbol due to the lack of a
+# allowlisting mechanism, we can still export them and tell users to
+# load it to make a future migration to pure Starlark easier.
+
+
+"""Adding missing bzlmod dependencies."""
+
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
 def remote_coverage_tools():
@@ -7,7 +31,7 @@ def remote_coverage_tools():
         urls = ["https://mirror.bazel.build/bazel_coverage_output_generator/releases/coverage_output_generator-v2.5.zip"],
     )
 
-def _coverage_deps_extension_impl(ctx):
+def _coverage_deps_extension_impl(_ctx):
     remote_coverage_tools()
 
 coverage_deps_ext = module_extension(