Updated graphics.rst

Updates based on the comments on GitHub

doc/src/vpr/graphics.rst

@@ -186,7 +186,8 @@ View Menu
 
     Items under view menu
 
-The view menu is displayed when there is a multi-layered architectures (more than 1 layer). 
+The view menu is displayed when vpr is targeting a stacked multi-die architecture (more than 1 layer).
+Layers are drawn in ascending order for many drawing features (e.g. blocks); that is layer 0 is drawn first, and (if visible), layer 1 is drawn on top of it etc.
 The visibility and transparency of a layer can be changed, which will affect blocks, nets, routing, and critical path.
 Cross-layer connections refer to connections that are in different layers.