Added flag for yield_ratio output

src/VTK/input_of_outputs.txt

@@ -15,6 +15,7 @@
 1  ! output e2d field at nodes
 1  ! output effective viscosity at elements 
 1  ! output whether element is plastic
+1  ! output elemental yield ratio
 1  ! output elemental dilatation rate
 0  ! output refinement criterion field
 1  ! output strain field