Added one more missing license header

Signed-off-by: Maciej Kurc <mkurc@antmicro.com>

vtr_xml_utils/__init__.py

diff --git a/vtr_xml_utils/__init__.py b/vtr_xml_utils/__init__.py
index e69de29..88e69cf 100644
--- a/vtr_xml_utils/__init__.py
+++ b/vtr_xml_utils/__init__.py
@@ -0,0 +1,10 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2020  The SymbiFlow Authors.
+#
+# Use of this source code is governed by a ISC-style
+# license that can be found in the LICENSE file or at
+# https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:  ISC