Update README.md, add pypi package badge

README.md

@@ -2,6 +2,7 @@
 
 ## Mongo backend for the stac-fastapi project built on top of the [sfeos](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch) core api library. 
 
+[![PyPI version](https://badge.fury.io/py/stac-fastapi.mongo.svg)](https://badge.fury.io/py/stac-fastapi.mongo)
 [![Join the chat at https://gitter.im/stac-fastapi-mongo/community](https://badges.gitter.im/stac-fastapi-mongo/community.svg)](https://gitter.im/stac-fastapi-mongo/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 To install from PyPI: