add link to wiki

README.md

@@ -20,8 +20,10 @@ Metrics and collections devised by CLIVAR ENSO group
 
 Planton, Y., E. Guilyardi, A. T. Wittenberg, J. Lee, P. J. Gleckler, T. Bayr, S. McGregor, M. J. McPhaden, S. Power, R. Roehrig,  J. Vialard, A. Voldoire, 2021: A New Way of Evaluating ENSO in Climate Models: The CLIVAR ENSO Metrics Package. Bulletin of the American Meteorological Society, 102, 1073-1080, [doi: 10.1175/BAMS-D-19-0337.A](https://doi.org/10.1175/BAMS-D-19-0337.A)
 
+Documentation for ENSO metrics: https://github.com/CLIVAR-PRP/ENSO_metrics/wiki
 
-## Release Notes and History
+
+### Release Notes and History
 
 | <div style="width:300%">[Versions]</div> | Update summary   |
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