Update README.md

Author: rwieruch

README.md

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 # react-local-storage
 
+[![Slack](https://slack-the-road-to-learn-react.wieruch.com/badge.svg)](https://slack-the-road-to-learn-react.wieruch.com/)
+
 Showcase on how to use the native `localStorage` of the browser to enable caching in React. Read more about it in [this tutorial](https://www.robinwieruch.de/local-storage-react/).
 
 ## Installation