Update how-to-create-and-use-shared-ptr-instances.md

[IceyPillow]

The old description about shared_ptr is wrong.

If we pass a raw ptr to a callee func, and use it to create a new shared_ptr, it's dangerous because callee will delete the resource where raw ptr pointed to.

Please accept this revision.

[prmerger-automator]

@Nowhere6 : Thanks for your contribution! The author(s) have been notified to review your proposed change.

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[ttorble]

@TylerMSFT

Can you review the proposed changes?

Important: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[learn-build-service-prod]

Learn Build status updates of commit af22544:

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[TylerMSFT]

Thank you for adding clarity around this scenario.

[learn-build-service-prod]

Learn Build status updates of commit e524ab0:

✅ Validation status: passed

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docs/cpp/how-to-create-and-use-shared-ptr-instances.md	✅Succeeded

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For any questions, please:

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[TylerMSFT]

#sign-off