miniyaml: document how to properly comment-out a node with child nodes

[phrohdoh]

ARTY:
    Inherits: ^TrackedVehicle
    Inherits@GAINSEXPERIENCE: ^GainsExperience
    Inherits@AUTOTARGET: ^AutoTargetGroundAssaultMove
    #Buildable:
    #    Queue: Vehicle
    #    BuildPaletteOrder: 230
    #    Prerequisites: dome, ~vehicles.allies, ...
    #    Description: ...