Docs: explain index files for server routing

[geromegrignon]

Describe the feature

The server routes documentation is missing a basic folder structure scenario, implying you are familiar with file-based routing structure.

It doesn't explain you can prefix files with index, like index.get.ts.

It unlocks using a folder for crud operations like:

articles
  - index.get.ts
  - index.post.ts
  - index.delete.ts

Or being able to cover routes like /articles and /articles/upcoming.

articles
  index.get.ts
  upcoming
    index.get.ts

Additional information

• Would you be willing to help implement this feature?

[pi0]

PR more than welcome to improve nitro docs 🙏🏼

[geromegrignon]

Awesome I wanted to wait for feedback from the team before starting working on it. I'll land a PR!