Add a feather file for use in docs. (#112)

Author: jjbrosnan

Iris/README.md

@@ -20,3 +20,7 @@ Fisher, R. A. ("The use of multiple measurements in taxonomic problems")[https:/
 
 Dua, D. and Graff, C. (2019). (UCI Machine Learning Repository)[http://archive.ics.uci.edu/ml]. Irvine, CA: University of 
 California, School of Information and Computer Science.
+
+## File formats
+
+A CSV and Feather file are made available.