Add NREL, PNNL, Leuven team.

contributors.md

@@ -1,7 +1,15 @@
 ## Contributors
 
-Thank you to all who have provided guidance on the development of this software. The following people have contributed directly to the development of this software (in alphabetical order):
+Thank you to all who have provided guidance on the development of this software. The following people have contributed directly to the development of this software and its design (in alphabetical order):
 
-- David H. Blum, Lawrence Berkeley National Laboratory
+- Javier Arroyo, KU Leuven
+- Kyle Benne, National Renewable Energy Laboratory
+- David Blum, Lawrence Berkeley National Laboratory
+- Yan Chen, Pacific Northwest National Laboratory
+- Lieve Helsen, KU Leuven
+- Sen Huang, Pacific Northwest National Laboratory
 - Filip Jorissen, KU Leuven
+- Yanfei Li, National Renewable Energy Laboratory
+- Draguna Vrabie, Pacific Northwest National Laboratory
 - Michael Wetter, Lawrence Berkeley National Laboratory
+