Getting started example improvements

[SORC3r3r]

I was using your "hello world" "Getting started" example on https://docs.marblejs.com/overview/getting-started and found some minor things missing in the setup.

I created all files and copied the content from your example.
One described step is to copy the following to the package.json

"scripts": {
  "start": "ts-node index.ts"
}

Maybe you can change it to "start": "ts-node server.ts" as the file is not named index.ts in your example.

For some it might also be helpful to add the line:
yarn add @marblejs/core @marblejs/middleware-logger @marblejs/middleware-body rxjs

[JozefFlakus]

Improved in #9 💪