Create contributing.md

Author: kevin-hirsch

.github/contributing.md

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+### What where you trying to do
+
+A few lines to explain the goal.
+
+### What actually happened
+
+A few lines to explain the bug.
+
+### What you think went wrong (optional)
+
+If you have an idea, don't hesitate to comment it here!
+
+### How to reproduce the issue
+
+Put some code here if necessary.
+
+### Details
+
+OS version, logs or screenshots.
+
+Thank you for your contribution! 👍