Add license badge to readme

Author: lucianopaz

README.md

@@ -4,6 +4,7 @@
 
 ![Build](https://github.com/pymc-labs/homepy/workflows/tests/badge.svg)
 [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
+[![License](https://img.shields.io/badge/License-Apache_2.0-mediumpurple.svg)](https://opensource.org/licenses/Apache-2.0)
 
 
 ## What does homepy do for you?