Create a file upload in Configuration/Site

Hi. I'm wondering where to paste this snippet that a file upload dialog appears?

I want to have the file upload field in Config/Site, put it in user/config/site.yaml but it didn't work... The upload doesn't appear.

This worked. Thanks to @paul_massendari in the slack channel.

user/blueprints/config/site.yaml

--- yaml
@extends:
'@parent'

form:
fields:
content:

        fields:
            my_files:
              type: file
              label: My Files
              multiple: true
              destination: 'user/download'
              random_name: false
              avoid_overwriting: false
              limit:
              filesize: 7 
              accept:
                - application/pdf