Add PyPi badge

Author: bradymholt

README.md

@@ -1,6 +1,6 @@
 # YNAB API Python Library
 
-[![Build](https://github.com/ynab/ynab-sdk-python/actions/workflows/build-test.yml/badge.svg)](https://github.com/ynab/ynab-sdk-python/actions/workflows/build-test.yml)
+[![Build](https://github.com/ynab/ynab-sdk-python/actions/workflows/build-test.yml/badge.svg)](https://github.com/ynab/ynab-sdk-python/actions/workflows/build-test.yml) [![PyPI version](https://badge.fury.io/py/ynab.svg?icon=si%3Apython)](https://badge.fury.io/py/ynab)
 
 This is the Python client for the YNAB API.