add contributing template

Author: Matthias-Schaub

docs/source/contributing.md

@@ -0,0 +1,12 @@
+# Contributing
+
+This document is a work progress. It should describe how to contribute (code or issues) to the MapSwipe back-end.
+
+To contribute to the MapSwipe back-end please create dedicated feature branches.
+
+```bash
+git checkout -b featureA
+git commit -am 'add new project type'
+git push -u origin featureA
+git request-pull origin/master featureA
+```