Update Set-MailUser.md

[Dean-Haas]

Added description per MAX work item 9515451. Note that there are several parameters that contain the placeholder {{ Fill XYZ Description }}

[learn-build-service-prod]

Learn Build status updates of commit 18062c9:

✅ Validation status: passed

File	Status	Preview URL	Details
exchange/exchange-ps/exchange/Set-MailUser.md	✅Succeeded	View (exchange-ps)

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 62f2112:

✅ Validation status: passed

File	Status	Preview URL	Details
exchange/exchange-ps/exchange/Set-MailUser.md	✅Succeeded	View (exchange-ps)

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