Create CONTRIBUTING.md in project root

Description

A CONTRIBUTING.md file in the root will be picked up while the creation of a Pull Request. This helps new users to hint to our guidelines again before they will create the PR. See https://github.com/blog/1184-contributing-guidelines for further details.

Environment

None
Fixed

Assignee

Patrice Bouillet

Reporter

Patrice Bouillet

Integrator

Stefan Siegl