Use REUSE framework (#3546)

* 📄 add licenses

* 👷 add REUSE compliance check

* 📝 add badge for REUSE

Co-authored-by: Florian Albrechtskirchinger <falbrechtskirchinger@gmail.com>

.reuse/README.md

@@ -0,0 +1,7 @@
+# REUSE Software
+
+This directory contains supporting files to make the project compliant with the REUSE specification.
+
+The root `Makefile` contains a target `reuse` that updates copyright headers and checks for compliance.
+
+See <http://reuse.software> for more information.