Add remark on result range to Thread.GetCurrentProcessorId() (#3770)

* Add remark on result range to `Thread.GetCurrentProcessorId()`

* Update xml/System.Threading/Thread.xml

Co-Authored-By: Jan Kotas <[email protected]>

Co-authored-by: Jan Kotas <[email protected]>

Author: 2 people

xml/System.Threading/Thread.xml

@@ -1858,6 +1858,8 @@ Main thread: ThreadProc.Join has returned.  Press Enter to end program.
 
 This value is cached and periodically refreshed. It may be stale by the time it's used: consuming code must not rely on its accuracy for correctness.
 
+The value is not guaranteed to be a zero-based processor number.
+
            ]]></format>
         </remarks>
       </Docs>