Update DataGuide_AAPF_HSI.md

DataGuide_AAPF_HSI.md

@@ -120,7 +120,12 @@ This section details the interpretation of an animated GIF file used to evaluate
 
 ### How to Read Information in Masterfile file (.xlsx, spreadsheet)
 
-The spreadsheets contains various phenotypic measurements derived from the HSI data and auxiliary measurement info. Here's a breakdown of the column headers:
+Phenotypic measurements derived from the HSI data and auxiliary measurements are stored in spreadsheets. The master data file (*.xlsx) is organized into two distinct groups:
+
+- `Vegetative_indices_Side`, `Vegetative_indices_Top`: This worksheet houses information on various vegetation indices calculated for side and top views.
+- `Reflectance_Side`, `Reflectance_Top`: This worksheet contains reflectance values at each measured wavelength, categorized by side and top views.
+
+Here's a breakdown of the column headers for the above worksheets:
 
 
 | Column Head          | Description                                           |