fixup! Generate Avro schema from AnVIL schema (#6109)

src/azul/service/avro_pfb.py

@@ -331,6 +331,14 @@ def pfb_schema_from_replicas(replicas: Iterable[JSON]
 
 def pfb_schema_from_anvil_schema(anvil_schema: JSON
                                  ) -> tuple[Sequence[str], JSON]:
+    """
+    Create a PFB schema for replicas of entities described by the AnVIL schema.
+    :param anvil_schema: A JSON document describing the tables and columns of
+                         the AnVIL metadata as stored in underlying repository.
+    :return: A tuple of
+             1. The set of entity types defined by the PFB schema
+             2. The PFB schema itself
+    """
     entity_schemas = []
     entity_types = []
     for table_schema in sorted(anvil_schema['tables'], key=itemgetter('name')):