add more badges to README

Author: drbenvincent

README.md

@@ -2,6 +2,9 @@
 
 [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
 [![PyPI version](https://badge.fury.io/py/CausalPy.svg)](https://badge.fury.io/py/CausalPy)
+![GitHub Repo stars](https://img.shields.io/github/stars/pymc-labs/causalpy?style=social)
+![Read the Docs](https://img.shields.io/readthedocs/causalpy)
+![PyPI - Downloads](https://img.shields.io/pypi/dm/causalpy)
 
 A Python package focussing on causal inference in quasi-experimental settings. The package allows for sophisticated Bayesian model fitting methods to be used in addition to traditional OLS.