Added Setups File and cleaned up Credits File

Hi Rod / Gents,

I've started doing a little work with Workshopper for a mini-project and figured in my case it was useful to have a setups / prerequisite installs part. I've added this and cleaned up the README to include this and document the CREDITS functionality.

Let me know if you think this is the best way to extend Workshopper.

Anyways greetings from Dublin and hope you're all doing well!

Eoin