Address review comment.

src-electron/generator/helper-zcl.js

@@ -310,7 +310,10 @@ async function zcl_struct_items_by_struct_name(name, options) {
 
 /**
  * Block helper iterating over all struct items given the struct name and
- * cluster name.
+ * cluster name.  The items iterated will be those that correspond to that
+ * struct name being used within the given cluster.  That means the struct name
+ * must be either a global struct (in which case the cluster name is just
+ * ignored), or a struct associated with the given cluster.
  *
  * @param name
  * @param clusterName