Fix menu order 9_adding-navigation.md

[plokko]

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[Amiejah]

@plokko Not sure if this PR is going to be picked up, but I believe that if any ordering method etc is missing we should add it to the HasPosition trait.

The MenuLink uses the HasPosition trait and this contains a scopeOrdered() method. So you could do something like:

MenuLink::published()->ordered()->get()->toTree()