Add comment to toml file

test/test_parameters_simplecrop.toml

@@ -40,4 +40,6 @@ insectmodel = ["season", "habitat", "pesticides"] # which factors affect insect
 [crop]
 cropmodel = "simple" # crop growth model to use, "almass", "aquacrop", or "simple"
 cropfile = "crop_data_general.csv" # file with general crop parameters
+# TODO: this parameter should be unnecessary, but removing it
+# currently gives an error
 growthfile = "almass_crop_growth_curves.csv" # file with crop growth parameters