[Story] Mac users see reference to "Alt +" in the shortcuts, but Mac's have no Alt key

[KludgeKML]

User story

As a Mac User
I want Mac-style modifer hints
So that I can use the keyboard navigation

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Acceptance criteria

This story is done when:

• Mac Users see "Option + ..." rather than "Alt + ..." for keyboard shortcuts, other users still see "Alt + ..."