Merge pull request hdl#230 from mithro/pdk-proto-BUILD

Add missing `BUILD` file in `pdk/proto` directory.

pdk/proto/BUILD

@@ -0,0 +1,23 @@
+# Copyright 2023 Google LLC
+#
+# 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.
+
+package(
+    default_applicable_licenses = ["//:package_license"],
+    default_visibility = ["//visibility:private"],
+)
+
+exports_files([
+    "build_defs.bzl",
+    "pdk_info.proto",
+])