SketchDependsOverrideAttribute example

Should give a concrete example of usage instead of an abstract suggestion.

_Originally posted by @Strowy in https://github.com/ActuatorDigital/Sketch/pull/30#discussion_r1277069442_

The issue names SketchDependsOverrideAttribute and points to the discussion on PR #30; start by reading that discussion and locating the existing abstract guidance in the documentation. Add a concrete usage example, then verify that the example matches the attribute’s documented behavior.

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