title: How to create an upload file field using react-final-form?
body: <p>I am trying to create an upload field ( class based ) using react-final-form</p>
  <p>Strangely documentation does not contain any info regarding this. Is there any way to implement this?</p>
  <p>I am getting a junk file link that is not useful to upload the file to the server.</p>
  <p>please help</p>