Document how to simulate multiple load cases with DAMASK

[gcapes]

A thread on slack suggested this as an example, but I'm not sure the syntax is documented anywhere in the official docs?

This will first do uniaxial, and then plane strain (in a single simulation!)

- schema: simulate_VE_loading_damask
  inputs:
    load_case::multistep:
      steps:
        - type: uniaxial
          total_time: 100
          num_increments: 800
          direction: x #L-stretching
          target_def_grad_rate: 1.0e-3
          dump_frequency: 200
        - type: plane_strain
          total_time: 100
          num_increments: 1200
          direction: xy # T-bending: loads in the x-direction with zero strain in the y-direction and zero stress in the z-direction
          target_def_grad_rate: 1.0e-3
          dump_frequency: 200

[gcapes]

Ah, it is kinda documented here:
https://docs.matflow.io/stable/reference/_autosummary/matflow.param_classes.load.LoadCase

but not in the most user-friendly way.