chore: add badge to readme

Author: lukasbach

readme.md

@@ -4,6 +4,7 @@
 ![](https://badgen.net/npm/types/react-complex-tree)
 [![](https://badgen.net/bundlephobia/dependency-count/react-complex-tree)](https://bundlephobia.com/package/react-complex-tree)
 [![](https://badgen.net/bundlephobia/minzip/react-complex-tree)](https://bundlephobia.com/package/react-complex-tree)
+[![npm downloads](https://badgen.net/npm/dt/react-complex-tree)](https://www.npmjs.com/package/react-complex-tree)
 
 [![Demo for React Complex Tree](https://raw.githubusercontent.com/lukasbach/react-complex-tree/main/demo.gif)](https://rct.lukasbach.com/docs/getstarted)