Clarify use of paragraphs in Script Events

[cconcolato]

Context: #300 (comment)

The spec says that a script event can contain "Zero or more Text objects, each being either Original or Translation"
In my use cases, there will be only at most 1 Original text object and at most 1 Translated text object (of a given language). The spec is not as strict as that, therefore you could theoretically have 2 original text objects and each text object could have a different represents attribute.
I would suggest adding text somewhere in the spec that describes the use case of 2 similar text objects in the same script event.