Statement why the Polyglot doc should be informative

Since the document should only document conclusions drawn from normative
statements made elsewhere, the Polyglot document itself should not be
normative, because there's a risk of erroneous conclusions getting held up
as normative and leading to confusion (especially since it's not a given
that change control on te Polyglot document is strictly enough controlled
to avoid errors and since there's a real risk of people asking for
restrictions stricter than the minimal logical consequences from normative
text elsewhere).