Add a CONTRIBUTING.MD

[RamReso]

In my opinion it is pretty nice to have a CONTRIBUTING.MD. This make contributing for a new contributor a little bit easier. I know that there is a section in the wiki, but this is a additional step one has to take if one already cloned the repo and made some changes. For me it would be enough to just have a link to this wiki page in the CONTRIBUTING.MD file.

[Hwurzburg]

adding to repo README would be worthwhile...I will post a PR...thanks