docs: add link to source in getting-started.md

I had a look at the "An Existing React App" chapter today. I found the code examples great, but was missing the link to the full code. To be honest I only "stumbled" to it via another page later. I think it's helpful if it's linked directly in this chapter.

Author: Nasicus

docs/introduction/getting-started.md

@@ -41,6 +41,8 @@ If you are using TypeScript, the React Redux types are maintained separately in
 npm install @types/react-redux
 ```
 
+The code used for this example is almost the same as the [official Redux+JS template](https://github.com/reduxjs/cra-template-redux). Additionally the same code template, but for typescript can be found [here](https://github.com/reduxjs/cra-template-redux-typescript).
+
 ## `Provider`
 
 React Redux includes a `<Provider />` component, which makes the Redux store available to the rest of your app: