mention phenotype dir in folder structure

src/schema/objects/files.yaml

@@ -102,6 +102,15 @@ derivatives:
     Derivative data (for example preprocessed files).
     See the [relevant section](SPEC_ROOT/common-principles.md#source-vs-raw-vs-derived-data)
     for more information.
+phenotype:
+  display_name: Phenotype
+  file_type: directory    
+  description: |
+    A directory where to store participant level measurements (for
+    example responses from multiple questionnaires) split into
+    individual files separate from `participants.tsv`.
+    See the [relevant section](SPEC_ROOT/modality-agnostic-files.md#phenotypic-and-assessment-data)
+    for more information.
 sourcedata:
   display_name: Source data
   file_type: directory