[feature request] Add ability to set accept attribute on file input

[mayjs]

Hi,

I've been using miniserve to scan important documents using my smartphone. For this, I serve a directory on my PC using miniserve (allowing file uploads). On my phone I take some pictures and upload them to this directory. Afterwards I use some shell scripts to post process the images to PDF and apply OCR to it.

I found that I could get my phone to offer the option to take a picture directly from the browser if the accept attribute of the file input was set to image/*.
Could this be something that other people would use as well? I'd be happy to create a PR with a new command line option to enable this attribute.