chore: adding a LICENSE file

one of the prerequisites for opening this project's source is a license file.
I'm choosing Apache2 because I have no reason to pick anything else.

Author: Shesekino

LICENSE

@@ -0,0 +1,14 @@
+Copyright 2019 Snyk Ltd.
+
+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.
+