Add Typescript section to Redux Toolkit Example (vercel#23166)

I have added a new section to the `with-redux-toolkit` example on setting up Typescript with Redux Toolkit and React-Redux.

It links the redux toolkit documentation and Next.js documentation on adding Typescript to a Next.js project.

examples/with-redux-toolkit/README.md

@@ -21,3 +21,9 @@ yarn create next-app --example with-redux-toolkit with-redux-toolkit-app
 ```
 
 Deploy it to the cloud with [Vercel](https://vercel.com/new?utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).
+
+### TypeScript Setup (optional)
+
+If you haven't already added [TypeScript](https://www.typescriptlang.org/) to your project, follow the [steps in the Next.js documentation](https://nextjs.org/docs/basic-features/TypeScript). If you are new to TypeScript, go through the Next.js [learning lesson on TypeScript](https://nextjs.org/learn/excel/TypeScript).
+
+Once TypeScript is added, follow the instructions given on the Redux Toolkit [documentation](https://redux-toolkit.js.org/tutorials/TypeScript) to set up and use Redux Toolkit and React-Redux with TypeScript