Update visualization.md (#2942)

* Update visualization.md

Added show_layer_names argument and its default value to docs

* Update visualization.md

docs/templates/visualization.md

@@ -10,9 +10,10 @@ from keras.utils.visualize_util import plot
 plot(model, to_file='model.png')
 ```
 
-`plot` takes one optional arguments:
+`plot` takes two optional arguments:
 
 - `show_shapes` (defaults to False) controls whether output shapes are shown in the graph.
+- `show_layer_names` (defaults to True) controls whether layer names are shown in the graph.
 
 You can also directly obtain the `pydot.Graph` object and render it yourself,
 for example to show it in an ipython notebook :