started a README.md, to have a place to document modelgen commands
diff --git a/xos/tools/README.md b/xos/tools/README.md
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+## Overview of XOS tools
+
+### modelgen
+
+Modelgen reads the XOS models and applies those models to a template to generate output.
+
+Examples:
+ * ./modelgen -a core api.template.py > ../../xos/xosapi.py
+ * ./modelgen -a services.hpc -b Service -b User hpc-api.template.py > ../../xos/hpcapi.py