Create SECURITY.md

[goxijana3]

Summary

Describe your changes here.

Fixes #Issue_Number (if available)

[dotnet-issue-labeler[bot]]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[dotnet-issue-labeler[bot]]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

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

Learn Build status updates of commit 31f0e3e:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
SECURITY.md	:white_check_mark:Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel