Explanatory comment from code review

Author: krivard

hhs_hosp/delphi_hhs/run.py

@@ -147,6 +147,10 @@ def smooth_values(df, smoother):
 def transform_signal(sensor, smoother, geo, df, geo_mapper):
     """Transform base df into specified geo/smoothing/prop configuration."""
     df = geo_mapper.add_geocode(df, "state_id", "state_code", from_col="state")
+    # handling population:
+    #   add population column
+    #   sum admission counts *and* population counts during make_geo
+    #   *then* divide counts by population to get the proportion 
     if sensor.endswith("_prop"):
         df=geo_mapper.add_population_column(df, "state_code")
     df = make_geo(df, geo, geo_mapper)