Add reference to source ArtGAN by CS CHAN

README.md

@@ -1,3 +1,17 @@
----
-license: apache-2.0
----
+---
+license: apache-2.0
+---
+Files from WikiArt, obtained from https://github.com/cs-chan/ArtGAN
+
+@article{artgan2018,
+  title={Improved ArtGAN for Conditional Synthesis of Natural Image and Artwork},
+  author={Tan, Wei Ren and Chan, Chee Seng and Aguirre, Hernan and Tanaka, Kiyoshi},
+  journal={IEEE Transactions on Image Processing},
+  volume    = {28},
+  number    = {1},
+  pages     = {394--409},
+  year      = {2019},
+  url       = {https://doi.org/10.1109/TIP.2018.2866698},
+  doi       = {10.1109/TIP.2018.2866698}
+}
+