Add contribution guide

CONTRIBUTING.md

+# Project Leads 
+
+- Marco Govoni (Argonne National Laboratory and University of Chicago)
+
+## Developers
+
+- He Ma (University of Chicago)
+- Han Yang (University of Chicago)
+- Huihuo Zheng (Argonne National Laboratory)
+
+## Contributors
+
+Aditya Tanikanti
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