Add badge to show number of project installations

Author: PaulRotmann

README.md

@@ -1,6 +1,7 @@
 # clue/stream-filter
 
 [![CI status](https://github.com/clue/stream-filter/workflows/CI/badge.svg)](https://github.com/clue/stream-filter/actions)
+[![Packagist downloads](https://img.shields.io/packagist/dt/clue/stream-filter?color=blue&label=installs)](https://packagist.org/packages/clue/stream-filter)
 
 A simple and modern approach to stream filtering in PHP