fix the minute gridder description (#11)

gridded_glm/libexec/_minute_gridder.py

 #!/usr/bin/env python3
 # Based on https://github.com/deeplycloudy/glmtools/blob/master/examples/grid/make_GLM_grids.py
 
-parse_desc = """Grid the past X minutes of GLM flash data, given a single input file.
+parse_desc = """Create one minute grids of GLM flash data.
 """
 
 import numpy as np