add licencing information to satisfy Reuse.
+<!--
+This file is part of JavaSMT,
+an API wrapper for a collection of SMT solvers:
+https://github.com/sosy-lab/java-smt
+
+SPDX-FileCopyrightText: 2020 Dirk Beyer <https://www.sosy-lab.org>
+
+SPDX-License-Identifier: Apache-2.0
+-->
+
# How to install Z3 for Windows64 for developers of JavaSMT
## Note:
