Improve Angular Testing Library API documentation

I am new to Angular Testing and stumbled across some misunderstandings while writing my first tests. I would like to help you improve it, so let's start collecting the issues. 🙂

1. The example for the declarations (within RenderOptions) is wrong. It configures the providers. Furthermore there is no descriptions for the providers option. https://testing-library.com/docs/angular-testing-library/api#declarations
2. We might also add a note which of the RenderOptions are passed to the Angular TestBed. Or even separate those from the added render properties.
3. Explaining that this library still works with the core testing functionality of Angular under the hood will also help to implement non-standard situations. For example in one test I needed to interact with a service. This can be done with the Angular TestBed: TestBed.get(TargetService).init();

Comienza con la documentación de la API de Angular Testing Library en la página enlazada de RenderOptions. Revisa el ejemplo de declarations, añade la descripción que falta de providers y aclara qué opciones se pasan a Angular TestBed y cómo TestBed puede admitir casos no estándar. Se considera terminado cuando los ejemplos y las notas explicativas cubren estos puntos con precisión.