Update README.md

Author: jginternational

README.md

@@ -1,6 +1,7 @@
 # KratosMultiphysics <-> GiD Interface
 
 [![Codacy Badge](https://app.codacy.com/project/badge/Grade/36d3d305c87e4bb398bc87ea2e3b890e)](https://www.codacy.com/gh/KratosMultiphysics/GiDInterface/dashboard?utm_source=github.com&amp;utm_medium=referral&amp;utm_content=KratosMultiphysics/GiDInterface&amp;utm_campaign=Badge_Grade)
+[![Tester](https://github.com/KratosMultiphysics/GiDInterface/actions/workflows/tester.yml/badge.svg)](https://github.com/KratosMultiphysics/GiDInterface/actions/workflows/tester.yml)
 
 The user interface of Kratos with [GiD](http://www.gidhome.com).