Examples do not reflect real-world use (data fetching is async)

# Describe the issue

The docs and examples talk about data being loaded from a database (which would be an asynchronous process), but they actually _show_ data generated _synchronously_, such as in [simple-usage/recipe.resolver](https://github.com/MichalLytek/type-graphql/blob/master/examples/simple-usage/recipe.resolver.ts#L17) where the source data (`items`) is available statically. In almost any real-world scenario, `createRecipeSamples` would be async.

# Are you able to make a PR that fix this?

Yes, once I have the knowledge.

# Additional context

Love the idea of this library!

Start with examples/simple-usage/recipe.resolver.ts at the createRecipeSamples usage and review the related documentation and examples that describe database-loaded data. Update the examples so their data-fetching behavior reflects asynchronous real-world use, then verify the example still works and its documentation matches.

Written by the indexing model from the issue text.