Improve doc of vtkColorTransferFunction::SetRange

Rendering/Core/vtkColorTransferFunction.h

@@ -429,12 +429,14 @@ protected:
    */
   int TableSize;
 
+  ///@{
   /**
    * Set the range of scalars being mapped. This method has no functionality
    * in this subclass of vtkScalarsToColors.
    */
   void SetRange(double, double) override {}
   void SetRange(const double rng[2]) override { this->SetRange(rng[0], rng[1]); }
+  ///@}
 
   /**
    * Internal method to sort the vector and update the