Update README.md

Author: matuskosut

README.md

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 # jupyter-brat-proxy
 
+[![PyPI - Python Version](https://img.shields.io/pypi/pyversions/jupyter-brat-proxy.svg)](https://pypi.org/project/jupyter-brat-proxy/)
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 ## Jupyter proxy
 
 Proxy extension that provides BRAT rapid annotation tool using [bratserver wrapper](https://pypi.org/project/bratserver/) in your Jupyterlab environment.