Add promotion Class Diagram

[nus-se-script]

Note from the teaching team: This bug was reported during the Part II (Evaluating Documents) stage of the PE. You may reject this bug if it is not related to the quality of documentation.

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Usage of # in the class diagram, which does not have any meaning. Probably a typo, meant to be a minus sign.

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_{[original: nus-cs2113-AY2324S2/pe-interim#2550] [original labels: type.DocumentationBug severity.VeryLow]}

[LowTL]

Team's Response

in a class diagram is a protected attribute, so it is labelled correctly.

Duplicate status (if any):

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