Add CI badge

It looks nice!

Signed-off-by: Gus Monod <[email protected]>

Author: Gus Monod

README.md

@@ -1,5 +1,7 @@
 # Python interface for Bloomberg's Comdb2 database
 
+[![Tests](https://github.com/bloomberg/python-comdb2/actions/workflows/build.yml/badge.svg)](https://github.com/bloomberg/python-comdb2/actions/workflows/build.yml)
+
 See [the Comdb2 documentation](https://bloomberg.github.io/comdb2/) for more
 information about the Comdb2 relational database, and then check out
 [the python-comdb2 documentation](https://bloomberg.github.io/python-comdb2/)