Add docs on where the settings file is

[zadjii-msft]

Also a note on focus mode, cause this happens frequently

Closes #719

[learn-build-service-prod[bot]]

Learn Build status updates of commit e35d90d:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
TerminalDocs/faq.yml	:white_check_mark:Succeeded	View

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