Add human statement to emphasize that _desc is the last entity

Closes bids-standard#1895

src/derivatives/common-data-types.md

@@ -25,7 +25,7 @@ A guide for using macros can be found at
 Preprocessed `bold` NIfTI file in the original coordinate space of the original run.
 The location of the file in the original datasets is encoded in the `Sources` metadata,
 and [`_desc-<label>`](../appendices/entities.md#desc)
-is used to prevent clashing with the original filename.
+is used (the last entity before the suffix) to prevent clashing with the original filename.
 
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 A guide for using macros can be found at