readme for atomfiles (mof force fields)

atomfiles/README.md

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+If you using any of these force-fields in your research, please cite our work!
+
+Science is hard, and force-fields are often more difficult to produce for complex materials than simply looking up values in a table.
+
+Thanks :)
+
+```
+https://onlinelibrary.wiley.com/doi/full/10.1002/adts.201900113?casa_token=Oq66FnSB9VYAAAAA%3A3g8o048QMb_K1WMxdZp-eK8JKeBL39vCE25_JLY_zjQ06T35beWg6UDrRqiix7YjCGvOmrddWNwrp0Ue
+```
+
+```
+Franz, Douglas M., et al. "MPMC and MCMD: Free High‐Performance Simulation Software for Atomistic Systems." Advanced Theory and Simulations 2.11 (2019): 1900113.
+```
+
+```
+Franz, D. M. et al. MPMC and MCMD: Free High‐Performance Simulation Software for Atomistic Systems. Adv. Theory Sim., 2019. DOI: 10.1002/adts.201900113
+```