change reference in README file

README

@@ -1,12 +1,8 @@
 This software is documented in:
 
-NCAR global model topography generation software for unstructured grids
-P. H. Lauritzen, J. T. Bacmeister, P. F. Callaghan, and M. A. Taylor
-Geosci. Model Dev. Discuss., 8, 4623-4651, 2015
-www.geosci-model-dev-discuss.net/8/4623/2015/
-doi:10.5194/gmdd-8-4623-2015
-
-http://www.geosci-model-dev-discuss.net/8/4623/2015/gmdd-8-4623-2015-discussion.html
+Peter H. Lauritzen, Julio T. Bacmeister, Patrick Callaghan and Mark A. Taylor, 2015: 
+NCAR Global Model Topography Generation Software for Unstructured Grids. 
+Geosci. Model Dev., 8, 3975-3986, doi:10.5194/gmd-8-3975-2015
 
 Overview
 ========
@@ -37,4 +33,4 @@ Remap elevation data to target grid and compute associated variables.
 4. cesm_meta_data_compliance:
 -----------------------------
 
-Python script to add CESM meta data to topography data file
+Python script to add CESM meta data to topography data file