[feature request] add text from clipboard, not only from file
Adding text using the data supplier API from a flat file and not only from JSON is great, but it would be even better if one could add text from the clipboard, not only from a file. 

Rationale: When I import real content into Sketch, I often don't have any file, it's more like "quickly grab some list from a web page or an email". Adding from the clipboard would skip the step of creating a temporary file.

If you're interested, I may give it a try (empasis on 'try', I'm no expert) and do a pull request.