[Content]: Better outline and information on FileRoutes

📚 Subject area/topic

SolidStart, FileRoutes

📋 Page(s) affected (or suggested, for new content)

https://docs.solidjs.com/solid-start/building-your-application/routing#file-based-routing

📋 Description of content that is out-of-date or incorrect

Users have expressed concerns regarding how file-based routing is documented. There isn't enough detail that's leading them to making mistakes:

Hey people can you help me with the nested routing while using FileRoutes
I have everything configured but nested route is showing page  not found

From our Discord where similar reports have been made a couple of times. What might be valuable is outlining nested routes in a clearer and more concise manner with more examples.

🖥️ Reproduction in StackBlitz (if reporting incorrect content or code samples)

No response

Ouvre la section FileRoutes sur la page de routage SolidStart liée et vérifie comment les routes imbriquées sont actuellement expliquées. Clarifie les indications sur le routage imbriqué à l’aide d’exemples concis et prends en compte le scénario page-not-found signalé ; le travail est terminé lorsque les utilisateurs peuvent comprendre la structure de fichiers et la configuration attendues.