Add 'plot element set' to examples or visualization section

Show how to plot element sets, either in the examples or in the visualization how-to. Something like

```python
plotter = pv.Plotter()
plotter.add_mesh(model.mesh.to_pyvista(), color="white", opacity=0.5)
plotter.add_mesh(element_set.mesh.to_pyvista(), color="green")
plotter.show()
```

Start by reviewing the existing examples and visualization how-to to choose the appropriate location for this material. Use the provided Python snippet as the basis, and consider the work done when users can find documented steps for plotting an element set alongside the model mesh.

Written by the indexing model from the issue text.