Missing documentation

Created by: depau

Hello @kkroening, I was going to make something like this for a work project, but then found your module. I gave a quick look and it seems pretty nice, but I see a only a few filters are supported and there's no documentation

Are you going to write any documentation for this and add more filters?

I may submit PRs to add a couple of them, I need effects like scale (zoom), sepia, greyscale and stuff like that, which I don't see.