make our help text return the name of the script that was actually called

Closes #19

gridded_glm/bin/cspp-geo-gglm-make-grids.sh

@@ -29,4 +29,5 @@ fi
 source $CSPP_GEO_GGLM_HOME/libexec/env.sh
 
 # Call the python module to do the processing, passing all arguments
+export PROG_NAME="${BASH_SOURCE[0]}"
 python3 $CSPP_GEO_GGLM_HOME/libexec/_make_glm_grids.py "$@"