add badges

Author: mahenzon

README.md

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+[![Documentation Status](https://readthedocs.org/projects/fastapi-jsonapi/badge/?version=latest)](https://fastapi-jsonapi.readthedocs.io/en/latest/?badge=latest)
+![PyPI](https://img.shields.io/pypi/v/fastapi-jsonapi?label=PyPI)
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 # FastAPI-JSONAPI
 
 FastAPI-JSONAPI is a FastAPI extension for building REST APIs.