Adding cross-repo include instructions

[Xelu86]

Contributor guide pull request

Thanks for contributing to the Microsoft Learn contributor guide. Please read these instructions for processing your pull request (PR). Once you've read this text, delete it and write a brief description of the changes you're proposing.

Quality control

• 1. Successful build with no warnings or errors: Review the build status to make sure all checks are green (Succeeded).

• 2. #Sign-off: Once the PR is finalized and ready to be merged, indicate so by typing #sign-off in a new comment in the PR. Signing off means the document is ready for review and can be published at any time.

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• All PRs to this repository are manually reviewed and merged.
• Once all feedback on the PR is addressed, we'll merge the PR into the main branch.

Need help?

If you have an open PR, tag the PR reviewers in a comment with your question: @mikekinsman, @jehchow

[learn-build-service-prod]

Learn Build status updates of commit 7467ad2:

✅ Validation status: passed

File	Status	Preview URL	Details
Contribute/content/markdown-reference.md	✅Succeeded	View

For more details, please refer to the build report.

[learn-build-service-prod]

PoliCheck Scan Report

The following report lists PoliCheck issues in PR files. Before you merge the PR, you must fix all severity-1 and severity-2 issues. The AI Review Details column lists suggestions for either removing or replacing the terms. If you find a false positive result, mention it in a PR comment and include this text: #policheck-false-positive. This feedback helps reduce false positives in future scans.

✅ No issues found

More information about PoliCheck

Information: PoliCheck | Severity Guidance | Term
For any questions: Try searching the learn.microsoft.com contributor guides or post your question in the Learn support channel.

[Xelu86]

Hello, the scope of this PR is to include cross-repo includes into the contributor guide.
#sign-off

[sgaspari815]

Closing PR with author permission. Content not needed in this guide.