added status badge for testing/CI

Author: cicirello

README.md

@@ -6,6 +6,7 @@ https://www.cicirello.org/
 
 [![DOI](http://joss.theoj.org/papers/10.21105/joss.00950/status.svg)](https://doi.org/10.21105/joss.00950)
 [![DOI](https://zenodo.org/badge/139182095.svg)](https://zenodo.org/badge/latestdoi/139182095)
+![Java CI](https://github.com/cicirello/JavaPermutationTools/workflows/Java%20CI/badge.svg)
 
 ## How to Cite