Update cpp/includes/defines.h

Co-authored-by: Alex H. Room <69592136+alexhroom@users.noreply.github.com>

Author: StephenNneji

cpp/includes/defines.h

@@ -557,7 +557,8 @@ numberOfContrasts : int
 geometry : str
     The geometry to use which can be 'air/substrate' or 'substrate/liquid'
 useImaginary : bool
-    Indicates whether imaginary component is used for the SLD value in layers.
+    Indicates whether imaginary component is used for the SLD value in layers, i.e.
+    absorption is set to True for the project.
 repeatLayers : list
     Information about repeating layers for each contrast
 contrastBackgroundParams : list