Add a "Usage with TypeScript" docs page

[markerikson]

Parent: #59

Copying over comments from #262 :

@phryneas:

As for the documentation page, writing just doesn't come to me today.
But I've created a codeSandbox with basically the content I would add to that page, without all the fancy words inbetween. If you're in a writing mood, could you take over from there?
https://codesandbox.io/s/rtk-ts-documentation-z8phk

Otherwise, I'll try again in a few days. That writing mood is unpredictable.

@markerikson:

I'm trying to convince myself to work on a blogpost atm, so I'm gonna hold off on trying to write docs for this.

Although having said that, the stuff I added to the Redux core "Usage with TS" looks fairly similar to where you're headed with that sandbox:

https://redux.js.org/recipes/usage-with-typescript#usage-with-redux-toolkit

And I like the outline that I see there.