update PACKAGE_README.md for beta1

Closes #18

gridded_glm/PACKAGE_README.md

 # CSPP Geo Gridded GLM
 
-USAGE
+CSPP Geo Gridded GLM takes GOES GLM Level 2 LCFA files and grids them to the ABI
+fixed grid. It does this using the open source glmtools python package by Eric Bruning.
 
-The following scripts are located in the `bin/` directory.
+More information can be found at:
 
-cspp-geo-gglm-trio-picker.sh
+https://github.com/deeplycloudy/glmtools
 
-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
+And the methods are described in Bruning et al. (2019):
 
-cspp-geo-gglm-minute-gridder.sh
+Bruning, E., Tillier, C. E., Edgington, S. F., Rudlosky, S. D., Zajic, J.,Gravelle, C., et al.
+(2019). Meteorological imagery for the Geostationary Lightning Mapper. Journal of Geophysical
+Research: Atmospheres, 2019; 124: 14285 14309. https://doi.org/10.1029/2019JD030874
 
-This script creates one minute grids from any number of input files.
+
+## USAGE
+
+cspp-geo-gglm.sh
+
+This script creates one minute grids from three GLM L2+ LCFA input files. It also has a "realtime"
+option where, provided a single input file, it will determine if an entire minute is available and
+begin gridding if appropriate.
 
 
 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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+This is a wrapper for the `make_GLM_grids.py` example utility provided by glmtools. Users may
+find this script useful for creating grids with custom resolutions or frame durations.
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