Per #1731, add more details about the grid-diag bin definition.

met/docs/Users_Guide/grid-diag.rst

@@ -93,6 +93,8 @@ _____________________
 
 The **name** and **level** entries in the **data** dictionary define the data to be processed. The **n_bins** parameter specifies the number of histogram bins for that variable, and the **range** parameter the lower and upper bounds of the histogram. The interval length is the upper and lower difference divided by **n_bins**.
 
+Each bin is inclusive on the left side and exclusive on the right, such as [a,b). Grid-Diag prints a warning message if the actual range of data values falls outside the range defined for that variable in the configuration file. Any data values less than or greater than the configured range are counted in the first or last bin, respectively.
+
 grid_diag output file
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