[TASK] Adds an example how to add attributes.

With that commit comes the ability to add a specific title and
description to an image directly while uploading them.

There is even more possible like adding links or alternative text or any
other already existing field in sys_file_reference table. Even
extending the sys_file_reference reference is possible and fill it up with custom
data. Just extend the FileReference model in your extension, assign your
content via the model setter in UploadedFileReferenceConverter and thats
it. Happy uploading.