Create Contributors Guide

[wegendt-bosch]

The goal of the contributors guide is to describe how to contribute to Mita.

• [x] Fork, Oomph clone, pull request, ... (the boring stuff, mostly copy/move from readme) @rherrmannr
  • [x] !Important: how to do ECA/Eclipse Account, sign-off!
• [x] Coding standard: blocks for if/else, xtend instead of java/...
• [x] Running/writing tests
• [x] Issue template/what to describe in issue

Place: wiki, link in readme

Lots of screenshots