Clarify to support nested typeDSL (#13)

Author: tom-tan

concepts.md

@@ -314,7 +314,8 @@ An implementation must resolve [$import](SchemaSalad.html#Import) and
 
 Another transformation defined in Schema salad is simplification of data type definitions.
 Type `<T>` ending with `?` should be transformed to `[<T>, "null"]`.
-Type `<T>` ending with `[]` should be transformed to `{"type": "array", "items": <T>}`
+Type `<T>` ending with `[]` should be transformed to `{"type": "array", "items": <T>}`.
+This simplification should be applied recursively.
 
 ## Extensions and metadata