Update README.md

Author: firefly-cpp

README.md

@@ -5,6 +5,7 @@
 [![PyPI Version](https://img.shields.io/pypi/v/fireflyalgorithm.svg)](https://pypi.python.org/pypi/fireflyalgorithm)
 ![PyPI - Python Version](https://img.shields.io/pypi/pyversions/fireflyalgorithm.svg)
 ![PyPI - Downloads](https://img.shields.io/pypi/dm/fireflyalgorithm.svg)
+[![Downloads](https://pepy.tech/badge/fireflyalgorithm)](https://pepy.tech/project/fireflyalgorithm)
 [![GitHub license](https://img.shields.io/github/license/firefly-cpp/FireflyAlgorithm.svg)](https://github.com/firefly-cpp/FireflyAlgorithm/blob/master/LICENSE)
 ![GitHub commit activity](https://img.shields.io/github/commit-activity/w/firefly-cpp/FireflyAlgorithm.svg)
 [![Average time to resolve an issue](http://isitmaintained.com/badge/resolution/firefly-cpp/FireflyAlgorithm.svg)](http://isitmaintained.com/project/firefly-cpp/FireflyAlgorithm "Average time to resolve an issue")