corrected explanation of [] in imported type description

Author: Toby Hodges

_episodes/19-custom-types.md

@@ -57,8 +57,9 @@ inputs:
 
 The reference to a custom type is a combination of the name of the file in which
 the object is defined (`InterProScan-apps.yml`) and the name of the object
-within that file (`apps`) that defines the custom type. The square brackets
-`[]` define the value of the imported type as an array.
+within that file (`apps`) that defines the custom type. The square brackets `[]`
+mean that an array of the preceding type is expected, in this case the `apps`
+type from the imported `InterProScan-apps.yaml` file
 
 The contents of the YAML file describing the custom type are given below: