Add a section giving credits to the original contributors

[DProvinciani]

Most of the rules in this repository were created for an old-deprecated repository. I see these rules were directly ported here.

In the next link, you can find a public fork of the original repository and see the contributors in the commits history. Many other contributors are missed in this fork so you should take them from the original repo.

https://github.com/lucianosmori/ExpertRules