[PE-D][Tester B] Wrong Example in Invalid Command

[nus-pe-script]

Describe the bug

• When writing an invalid command for adding an appointment, the examples that shows up does not contain the prefix input which are add_a.

To Reproduce

1. input add_a in the command input box.

Expected Behaviour The example should also shows the prefix which are add_a

Screenshot

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Labels: type.DocumentationBug severity.VeryLow original: angkyakdifp/ped#8

[derekjxtan]

valid, to update error message