Add fork README

Author: jomey

README.md

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+# Fork of the Spatial Modeling for Resources Framework (SMRF)
+
+This is a fork of the [USDA-ARS-NWRC SMRF](https://github.com/USDA-ARS-NWRC/smrf)
+repo with the model development state used for publication in
+[Geoscientific Model Development](https://gmd.copernicus.org/).
+
+The original repo README [can be found here](README_smrf.md)