Update CONTRIBUTING.md

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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+* Verena Weiler (verena.weiler@steinbeis.de)
+* Reiner Braun (reiner@formenformen.com)
+* Volker Coors (volker.coors@stw.de)