Add comment explaining time shift, in both places it happens

reports/glides_terminal_missed_extraneous_predictions.livemd

@@ -502,6 +502,7 @@ times_table =
 
 trips_table =
   0..23
+  # Service day starts at 4am, so let's start the table at that hour.
   |> Enum.map(&rem(&1 + 4, 24))
   |> Enum.map(fn hour ->
     predicted_trip_count =
@@ -559,4 +560,4 @@ Kino.Download.new(
 Kino.DataTable.new(trips_table, name: trips_table_name)
 ```
 
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