Update README.md

Author: csko

README.md

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 # GDAX Python API
 
 [![Build Status](https://travis-ci.org/csko/gdax-python-api.svg?branch=master)](https://travis-ci.org/csko/gdax-python-api)
+[![PyPI](https://img.shields.io/pypi/pyversions/gdax-python-api.svg)]()
+[![PyPI](https://img.shields.io/pypi/v/gdax-python-api.svg)]()
 
 Unofficial GDAX API client written in Python3 using async/await