Add REUSE badge in README

Author: flashcode

README.md

@@ -3,6 +3,7 @@
 [![PyPI](https://img.shields.io/pypi/v/msgcheck.svg)](https://pypi.org/project/msgcheck/)
 [![Build Status](https://github.com/flashcode/msgcheck/workflows/CI/badge.svg)](https://github.com/flashcode/msgcheck/actions?query=workflow%3A%22CI%22)
 [![Build Status](https://github.com/flashcode/msgcheck/workflows/CodeQL/badge.svg)](https://github.com/flashcode/msgcheck/actions?query=workflow%3A%22CodeQL%22)
+[![REUSE status](https://api.reuse.software/badge/github.com/flashcode/msgcheck)](https://api.reuse.software/info/github.com/flashcode/msgcheck)
 
 Msgcheck performs various checks on gettext files (with extension `.po`):