added tests badge to README

Author: tclose

README.md

@@ -1,5 +1,7 @@
 # Pydra Tasks for mrtrix3
 
+[![Python package](https://github.com/nipype/pydra-mrtrix3/actions/workflows/pythonpackage.yml/badge.svg)](https://github.com/nipype/pydra-mrtrix3/actions/workflows/pythonpackage.yml)
+
 ## For developers
 
 Install repo in developer mode from the source directory. It is also useful to