Mention that `Component.render` could return iterator

According to the discussion here https://github.com/facebook/react/issues/11502 it is legal to return iterators from Component.render. But it is not mentioned in the document.

Moreover -- it would work only in production mode, not in development. It should me mentioned that to make it work in both environments -- you should use iterable, rather than iterator (see this Seq approach from the Reach issue).

I suggest to place it around https://reactjs.org/docs/react-component.html#fragments

Commencez par la documentation de React Component dans la section liée react-component.html#fragments, puis lisez le React issue lié et sa discussion Seq sur le comportement de iterator et iterable. Mettez à jour la documentation pour mentionner que Component.render peut renvoyer un iterator, expliquer la limitation propre à production et recommander un iterable pour un comportement cohérent dans les deux environnements.