add the most basic of READMEs

gridded_glm/PACKAGE_README.md

 # CSPP Geo Gridded GLM
 
-TODO
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+USAGE
+
+The following scripts are located in the `bin/` directory.
+
+cspp-geo-gglm-trio-picker.sh
+
+A simple wrapper around cspp-geo-gglm-minute-gridder.sh that takes a single input file and:
+1) determines if it is the last file in a minute
+2) if so, finds all files from that minute and passes them to cspp-geo-gglm-minute-gridder.sh
+3) creates both grids and tiles for that minute
+
+cspp-geo-gglm-minute-gridder.sh
+
+This script creates one minute grids from any number of input files.
+
+
+cspp-geo-gglm-make-grids.sh
+
+A wrapper for the `make_GLM_grids.py` "kitchen sink" example script provided by glmtools.
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