title: plotting several grids with pyvista
body: <p>I have several meshes I read each of them using pyvista</p>
  <pre><code>import pyvista as pv
  
  # read the data
  grid1 = pv.read('mesh1.vtk')
  grid2 = pv.read('mesh2.vtk')
  </code></pre>
  <p>I want to plot them together on same plot having different colors
  I do :</p>
  <pre><code>plotter = pv.Plotter(window_size=(1500, 1100))
  plotter.add_mesh(grid1, color=[0.6, 0.2, 0.1])
  plotter.add_mesh(grid2, color=[0.1, 0.6, 0.6])
  </code></pre>
  <p>Can I add label for each grid? or add legend?</p>