Add CONTRIBUTING

CONTRIBUTING.md

+The Dutch Building Physics Library was developed by the Steinbeis Transferzentrum Technische Beratung an der HFT Stuttgart.
+
+Verena Weiler (verena.weiler@steinbeis.de)
+Reiner Braun (reiner@formenformen.com)
+Volker Coors (volker.coors@stw.de)
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