GC.SuppressFinalize clarification (#3279)

Author: mairaw

xml/System/GC.xml

@@ -1415,7 +1415,9 @@ This method is most useful in monitoring scenarios for measuring the difference
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 ## Remarks  
- This method sets a bit in the object header of `obj`, which the runtime checks when calling finalizers. A finalizer, which is represented by the <xref:System.Object.Finalize%2A?displayProperty=nameWithType> method, is used to release unmanaged resources before an object is garbage-collected. If `obj` does not have a finalizer, the call to the <xref:System.GC.SuppressFinalize%2A> method has no effect.  
+
+This method sets a bit in the object header of `obj`, which the runtime checks when calling finalizers. A finalizer, which is represented by the <xref:System.Object.Finalize%2A?displayProperty=nameWithType> method, is used to release unmanaged resources before an object is garbage-collected. 
+If `obj` does not have a finalizer or the GC has already signaled the finalizer thread to run the finalizer, the call to the <xref:System.GC.SuppressFinalize%2A> method has no effect.  
   
  Objects that implement the <xref:System.IDisposable> interface can call this method from the object's <xref:System.IDisposable.Dispose%2A?displayProperty=nameWithType> implementation to prevent the garbage collector from calling <xref:System.Object.Finalize%2A?displayProperty=nameWithType> on an object that does not require it. Typically, this is done to prevent the finalizer from releasing unmanaged resources that have already been freed by the <xref:System.IDisposable.Dispose%2A?displayProperty=nameWithType> implementation.