Update README.md

Author: rwieruch

README.md

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 # react-graphql-github-vanilla
 
+[![Slack](https://slack-the-road-to-learn-react.wieruch.com/badge.svg)](https://slack-the-road-to-learn-react.wieruch.com/)
+
 A simple React application consuming the GitHub GraphQL API with plain HTTP requests. [Read more about it over here](https://www.robinwieruch.de/react-with-graphql-tutorial).
 
 ## Features