Add CI status

Author: rocky

README.rst

@@ -1,4 +1,4 @@
-|Pypi Installs| |Latest Version| |Supported Python Versions|
+|CI status| |Pypi Installs| |Latest Version| |Supported Python Versions|
 
 mathicsscript is a command-line interface to Mathics.
 
@@ -51,3 +51,4 @@ goes wrong, it is harder to track down problems.
 		 :target: https://badge.fury.io/py/mathicsscript
 .. |Pypi Installs| image:: https://pepy.tech/badge/mathicsscript
 .. |Supported Python Versions| image:: https://img.shields.io/pypi/pyversions/mathicsscript.svg
+.. |CI status| image::https://github.com/Mathics3/mathicsscript/workflows/mathicsscript%20(basic)/badge.svg