Update readme.md

Author: moritzmock

readme.md

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 React Toolbox
 =============
 
+[![npm version](https://badge.fury.io/js/%40aboutbits%2Freact-toolbox.svg)](https://badge.fury.io/js/%40aboutbits%2Freact-toolbox)
+
 This package includes different tools that support you with common tasks.
 
 ## Table of content