[Docs] add example of index using annotations
[Docs] add example of index using annotations

loic425/Sylius,SyliusBot/Sylius,Zales0123/Sylius,antonioperic/Sylius,lchrusciel/Sylius,lchrusciel/Sylius,diimpp/Sylius,lchrusciel/Sylius,Sylius/Sylius,Sylius/Sylius,diimpp/Sylius,101medialab/Sylius,antonioperic/Sylius,Sylius/Sylius,antonioperic/Sylius,diimpp/Sylius,101medialab/Sylius,Zales0123/Sylius,SyliusBot/Sylius,loic425/Sylius,loic425/Sylius,Zales0123/Sylius,SyliusBot/Sylius,101medialab/Sylius