Change the doc linked to for Activity.ID details (#8705)

Author: samsp-msft

xml/System.Diagnostics/Activity.xml

@@ -818,7 +818,7 @@ Normally if the <xref:System.Diagnostics.Activity.ParentId> is defined, its form
 
 ## Remarks
 
-An ID has a hierarchical structure: `root-id.id1_id2.id3_`. The ID is generated when <xref:System.Diagnostics.Activity.Start> is called by appending a suffix to the `Activity.Parent.Id` or the <xref:System.Diagnostics.Activity.ParentId>. An <xref:System.Diagnostics.Activity> has no ID until it starts. For more information, see [Id Format](https://github.com/dotnet/runtime/blob/main/src/libraries/System.Diagnostics.DiagnosticSource/src/ActivityUserGuide.md#id-format).
+An ID has a hierarchical structure: `root-id.id1_id2.id3_`. The ID is generated when <xref:System.Diagnostics.Activity.Start> is called by appending a suffix to the `Activity.Parent.Id` or the <xref:System.Diagnostics.Activity.ParentId>. An <xref:System.Diagnostics.Activity> has no ID until it starts. For more information, see [Activity IDs](/dotnet/core/diagnostics/distributed-tracing-concepts#activity-ids).
 
 ]]></format>
         </remarks>