Add text at a coordinate.

        Args:
            coords: Coordinates to add text at.
            text: Text to place.
            color: Color for text as RGB. Defaults to black.

def add_text(self, coords, text, color=(0, 0, 0)):
        """
        Add text at a coordinate.

        Args:
            coords: Coordinates to add text at.
            text: Text to place.
            color: Color for text as RGB. Defaults to black.
        """
        source = vtk.vtkVectorText()
        source.SetText(text)
        mapper = vtk.vtkPolyDataMapper()
        mapper.SetInputConnection(source.GetOutputPort())
        follower = vtk.vtkFollower()
        follower.SetMapper(mapper)
        follower.GetProperty().SetColor(color)
        follower.SetPosition(coords)
        follower.SetScale(0.5)
        self.ren.AddActor(follower)
        follower.SetCamera(self.ren.GetActiveCamera())