Update README.md

Author: searchivarius

README.md

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 [![PyPI version](https://img.shields.io/pypi/v/pyfastpfor.svg)](https://pypi.python.org/pypi/pyfastpfor/)
+[![Downloads](https://pepy.tech/badge/pyfastpfor)](https://pepy.tech/project/pyfastpfor)
+[![Downloads](https://pepy.tech/badge/pyfastpfor/month)](https://pepy.tech/project/pyfastpfor/month)
 [![Build Status](https://travis-ci.org/searchivarius/PyFastPFor.svg?branch=master)](https://travis-ci.org/searchivarius/PyFastPFor)
 # PyFastPFor
 Python bindings for the fast **light-weight** integer compression library [FastPFor](https://github.com/lemire/FastPFor): A research library with integer compression schemes. FastPFor is broadly applicable to the compression of arrays of 32-bit integers where most integers are small. The library seeks to exploit SIMD instructions (SSE) whenever possible. This library can decode at least 4 billions of compressed integers per second on most desktop or laptop processors. That is, it can decompress data at a rate of 15 GB/s. This is significantly faster than generic codecs like gzip, LZO, Snappy or LZ4.