Fix typo and clarify NU1507 warnings explanation

[anderson-joyle]

Corrected a typo and clarified the explanation regarding NU1507 warnings and NuGet.config file conflicts.

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[learn-build-service-prod]

Learn Build status updates of commit d816229:

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File	Status	Preview URL	Details
task-reference/dotnet-core-cli-v2.md	✅Succeeded

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