fix: add desc- entity name into descriptions.tsv example

consistent with other uses of {ent}_id -- like session_id, participant_id etc,
and per description for the column already saying
"A desc-<label> entity present in the derivatives dataset."

This would be another good use case for uprade/migrate command to fixup those

Author: yarikoptic

src/derivatives/common-data-types.md

@@ -331,9 +331,9 @@ Contents of the `descriptions.tsv` file:
 
 ```tsv
 desc_id	description
-Filt	low-pass filtered at 30Hz
-FiltDs	low-pass filtered at 30Hz, downsampled to 250Hz
-preproc	low-pass filtered at 30Hz, downsampled to 250Hz, and rereferenced to a common average reference
+desc-Filt	low-pass filtered at 30Hz
+desc-FiltDs	low-pass filtered at 30Hz, downsampled to 250Hz
+desc-preproc	low-pass filtered at 30Hz, downsampled to 250Hz, and rereferenced to a common average reference
 ```
 
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