Added note about non-primary-key GUIDs. (#792)

* Added note about non-primary-key GUIDs.

Author: mkincaid-bw

docs/contributing/code-style/csharp.md

@@ -180,10 +180,17 @@ timestamp information for sequential ordering.
 // Good
 var id = CoreHelpers.GenerateComb();
 
-// Bad
+// Bad - for entity IDs, don't use Guid.NewGuid()
 var id = Guid.NewGuid();
 ```
 
+:::note
+
+For non-primary-key GUIDs (e.g. correlation IDs or other values not used as a database primary key),
+`Guid.NewGuid()` is acceptable.
+
+:::
+
 Entities should implement `SetNewId()`:
 
 ```csharp