add testing badge

Author: robertjwilson

README.md

@@ -1,5 +1,7 @@
 [![Documentation Status](https://readthedocs.org/projects/oceanval/badge/?version=latest)](https://oceanval.readthedocs.io/en/latest/?badge=latest)
 [![Conda Badge](https://anaconda.org/conda-forge/oceanval/badges/version.svg)](https://anaconda.org/channels/conda-forge/packages/oceanval/overview)
+![GitHub Testing](https://github.com/pmlmodelling/oceanVal/actions/workflows/python-app-linux.yml/badge.svg)
+
 
 
 # oceanVal