[Request]: Add Form File Upload Section to Router Docs

[MatthewIsHere]

What is this request related to?

Request

📋 Suggested

https://docs.solidjs.com/solid-router/concepts/actions#using-forms-to-submit-data

📋 General description or bullet points

I believe it would be helpful to add a footnote or section that uploading a file requires attribute enctype="multipart/form-data" on the form in order for actions to receive the file. A small section at the bottom of the code example could mention the usage.

I know this is not technically a Solid/Router issue, but I believe it would clear up any errors from new solid-start users. I would be happy to submit a PR, but I wanted to float the idea first.

🖥️ Reproduction of code samples in StackBlitz

No response