Fixes #11978 - Create new article about parallel execution

[sdwheeler]

PR Summary

Create new article about parallel execution

• Fixes AB#431947
• Fixes Better documentation on improving/parallelizing script performance #11978

PR Checklist

• Descriptive Title: This PR's title is a synopsis of the changes it proposes.
• Summary: This PR's summary describes the scope and intent of the change.
• Contributor's Guide: I have read the contributors guide.
• Style: This PR adheres to the style guide.

[learn-build-service-prod]

Learn Build status updates of commit 2bc5e67:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/dev-cross-plat/performance/parallel-execution.md	✅Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/toc.yml	✅Succeeded	View (>=powershell-5.1)

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

[learn-build-service-prod]

Learn Build status updates of commit a5c6f49:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/dev-cross-plat/performance/parallel-execution.md	✅Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/toc.yml	✅Succeeded	View (>=powershell-5.1)

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

[santisq]

New doc looks great! Thanks for taking the time guys!