Added citation.

README.md

@@ -10,6 +10,15 @@ open-source program for enumerating small-molecule ionization states.
 
 Users can provide SMILES strings from the command line or via an .smi file.
 
+Citation
+--------
+
+If you use Dimorphite-DL in your research, please cite:
+
+Ropp PJ, Kaminsky JC, Yablonski S, Durrant JD (2019) Dimorphite-DL: An
+open-source program for enumerating the ionization states of drug-like small
+molecules. J Cheminform 11:14. doi:10.1186/s13321-019-0336-9.
+
 Licensing
 ---------
 

dimorphite_dl.py

@@ -33,6 +33,12 @@ except ImportError:
 # Always let the user know a help file is available.
 print("\nFor help, use: python dimorphite_dl.py --help")
 
+# And always report citation information.
+print("\nIf you use Dimorphite-DL in your research, please cite:")
+print("Ropp PJ, Kaminsky JC, Yablonski S, Durrant JD (2019) Dimorphite-DL: An")
+print("open-source program for enumerating the ionization states of drug-like small")
+print("molecules. J Cheminform 11:14. doi:10.1186/s13321-019-0336-9.\n")
+
 try:
     import rdkit
     from rdkit import Chem