Mention gss-ntlmssp package for NTLM on Linux

[rzikm]

Closes dotnet/runtime#101058.

[rzikm]

CC: @wfurt

[learn-build-service-prod]

Learn Build status updates of commit 6796e89:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Net/NetworkCredential.xml	✅Succeeded	View

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accidentally approved

[learn-build-service-prod]

Learn Build status updates of commit 1379295:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Net/NetworkCredential.xml	✅Succeeded	View

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 c49061e:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Net/NetworkCredential.xml	✅Succeeded	View

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 465d954:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Net/NetworkCredential.xml	✅Succeeded	View

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

[wfurt]

LGTM. thanks.