update readme with zenodo doi link

README.md

@@ -4,6 +4,8 @@
 [![Latest Version](https://img.shields.io/pypi/v/psiturk.svg?style=flat-square&label=latest%20stable%20version)](https://pypi.python.org/pypi/psiturk/)
 [![Coverage Status](https://coveralls.io/repos/github/NYUCCL/psiTurk/badge.svg?branch=master)](https://coveralls.io/github/NYUCCL/psiTurk?branch=master)
 [![License](http://img.shields.io/badge/license-MIT-red.svg)](http://en.wikipedia.org/wiki/MIT_License)
+[![DOI](https://zenodo.org/badge/4845420.svg)](https://zenodo.org/badge/latestdoi/4845420)
+
 
 Please visit [psiturk.org](https://psiturk.org) for more information.
 
@@ -37,10 +39,13 @@ A test suite can be run using `pytest` from within the base directory of psiturk
 
 # Citing 
 
-You are welcome to use this code for personal or academic uses. If you fork,
-or use this in an academic paper please cite as follows:
+To credit psiTurk in your work, please cite both the original conference paper and a version of the Zenodo archive.
+The former provides a high level description of the package, and the latter points to a permanent record of all psiTurk
+versions (we encourage you to cite the specific version you used). Example citations (for psiTurk 2.3.7):
+
+Eargle, David, Gureckis, Todd, Rich, Alexander S., McDonnell, John, & Martin, Jay B. (2020, January 6). 
+psiTurk: An open platform for science on Amazon Mechanical Turk (Version v2.3.7). Zenodo. http://doi.org/10.5281/zenodo.3598652
 
 McDonnell, J.V., Martin, J.B., Markant, D.B., Coenen, A., Rich, A.S., and Gureckis, T.M. 
 (2012). psiTurk (Version 1.02) [Software]. New York, NY: New York University. 
-Available from https://github.com/NYUCCL/psiTurk
-
+Available from https://github.com/NYUCCL/psiTurk