Add a motivation or why use section to readme

[morenoh149]

Hello, I am curious about this project. But it is unclear to me what it does exactly and when would I want to use it.

I suspect I could use this to allow visitors of my django webapp to upload files directly to s3 using signed urls. But then you show a screenshot of the django admin panel. If you could clarify what this package does I'd be happy to adda a paragraph at the top of the readme explaining the package.