Update the matcha_kelvin_verilog genrule to add OSS header

Change-Id: I9c1af4ad870723b41677dd636475125b10bdb485

hdl/chisel/BUILD

diff --git a/hdl/chisel/BUILD b/hdl/chisel/BUILD
index 11c0dcd..8277e44 100644
--- a/hdl/chisel/BUILD
+++ b/hdl/chisel/BUILD
@@ -181,7 +181,21 @@
     srcs = [":Kelvin.v"],
     outs = ["kelvin.v"],
     cmd = """
-    echo "// SHA: $$(awk '/KELVIN_BUILD_GIT_VERSION/ { print $$2 }' \
+    echo "// 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.
+
+// SHA: $$(awk '/KELVIN_BUILD_GIT_VERSION/ { print $$2 }'\
       bazel-out/volatile-status.txt)" > $@
     cat $< >> $@
     """,