be more precise on the default cardinality context

Reading the "managed composition" part made me first think of the
Orders:Items element when talking about the cardinality, but that's
to-many, which had me wondering for a sec. But I think what's being
referred to here is the backlink, i.e. this `up_` element:

```yaml
  Orders.Items:
    kind: entity
    includes: [OrderItems]
    elements:
      up_:
        key: true
        type: cds.Association
        cardinality: { min: 1, max: 1 }
        target: Orders
        keys: [{ ref: [ID] }]
        notNull: true
```

Author: qmacro

cds/cdl.md

@@ -1040,7 +1040,7 @@ aspect OrderItems {
 
 #### Default Target Cardinality
 
-If not otherwise specified, a managed composition of an aspect has the default target cardinality *to-one*.
+If not otherwise specified, a managed composition of an aspect has the default target cardinality *to-one* for the backlink.
 
 #### For Many-to-many Relationships