Merge pull request #29 from SimonFrings/installations

Add badge to show number of project installations

Author: clue

README.md

@@ -1,6 +1,7 @@
 # PromiseStream
 
 [![CI status](https://github.com/reactphp/promise-stream/workflows/CI/badge.svg)](https://github.com/reactphp/promise-stream/actions)
+[![installs on Packagist](https://img.shields.io/packagist/dt/react/promise-stream?color=blue&label=installs%20on%20Packagist)](https://packagist.org/packages/react/promise-stream)
 
 The missing link between Promise-land and Stream-land
 for [ReactPHP](https://reactphp.org/).