Add more for instructions for manual testing

[nus-pe-bot]

Instructions for manual testing is extremely minimal, and could definitely be improved since this app has a lot of features.

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_{[original: nus-cs2103-AY2425S1/pe-interim#3907] [original labels: severity.Low type.DocumentationBug]}

[RezwanAhmed123]

Team's Response

Thanks for bringing this up. This makes sense and will be done in a future update!

Duplicate status (if any):

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