Document file_engine in the docs guide on user input

[MassiminoilTrace]

At the https://dioxuslabs.com/learn/0.4/reference/user_input page, there's no mention on how to use input fields with type="file".
Trying to print the oninput event using the debug formatting didn't help either, as only empty "value" and "values" fields did show up.
Then I found the existence of the files field from the docs generated by cargo doc, in the dioxus::prelude::FormData. After more searching, I found this other example showing file upload https://github.com/Demonthos/dioxus/blob/master/examples/file_upload.rs

I would suggest documenting the file input feature inside the "user_input" guide page at https://dioxuslabs.com/learn/0.4/reference/user_input page.

Can I help in some way? Be warned that I'm not a native english speaker, so a checking might be needed anyway.

[ealmloff]

That sounds like a great addition! Most of dioxus' events mirror the web api, so we don't have documentation on all events in the reference. It makes sense to at least document the file engine because it is significantly different from what you may use in javascript.

Can I help in some way? Be warned that I'm not a native english speaker, so a checking might be needed anyway.

If you would like to add a section to the user_input documentation, I would be happy to check it!

[MassiminoilTrace]

Closed with #102