tag added to ReadMe

Author: konstntokas

README.md

@@ -1,5 +1,6 @@
 # xcube-resampling
 
+[![Build Status](https://github.com/xcube-dev/xcube-resampling/actions/workflows/unit-tests.yml/badge.svg?branch=main)](https://github.com/xcube-dev/xcube-resampling/actions/workflows/unit-tests.yml)
 [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
 
 **xcube-resampling** provides efficient algorithms for transforming datasets into