Add DOI to README

Author: mwaskom

README.md

@@ -45,6 +45,11 @@ The documentation has an [example gallery](http://stanford.edu/~mwaskom/software
 
 - [Plotting statistical timeseries data](http://nbviewer.ipython.org/github/mwaskom/seaborn/blob/master/examples/timeseries_plots.ipynb)
 
+Citing
+------
+
+Seaborn can be cited using a DOI provided through Zenodo: [![DOI](https://zenodo.org/badge/doi/10.5072/zenodo.12710.png)](http://dx.doi.org/10.5072/zenodo.12710)
+
 
 Dependencies
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