Ad-hoc, non-file sidecar

[roachcord3]

Not sure how best to describe this so I'll just say my user story. I would like to be able to define a sidecar on import that doesn't exist as a file already in the import folder, primarily so that I can associate URLs up front when importing extracted RAR files from gumroad and other sites where the result of the download is an archive, not the files that will be imported. Manually crafting sidecar files would be more time consuming than an option to do it all in-client. I'm requesting this as a sidecar and not "add URLs like tags" because a generic design would let people also do something like this for notes if they wanted.