Added CodeSandBox.io into the tools section of the readme.md file

Author: darkdaante

README.md

@@ -149,6 +149,7 @@ Useful articles and learning resources.
 - [Create React App](https://github.com/facebook/create-react-app) - Create React apps with no build configurations.
 - [Swagger](https://swagger.io/) - Design and document APIs compatible with OpenAPI specification.
 - [StackEdit](https://stackedit.io/) - In-browser Markdown editor
+- [CodeSandBox](https://codesandbox.io/) - An Online IDE for rapid web development with live preview and support for npm packages. 
 
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