Document how to import texture by loading orientations from a file

[gcapes]

Following a recent discussion, it seems that this isn't documented anywhere. I'm not sure where this would fit in the current documentation - perhaps as a demo workflow?
The closest match I can see is https://docs.matflow.io/stable/user/getting_started/custom_task_schemas_and_workflows.html#passing-variables-around-a-workflow but that isn't the right place. I think this might actually be for hpcflow, because the script run by the task schema below expects orientations as an input so the handling of where this input comes from must happen "upstream" i.e. in hpcflow.

Maybe there should be another syntax section where we can define all the options and give some examples. It would also be a suitable place for #485

  - schema: generate_volume_element_from_voronoi
    inputs:
      homog_label: SX
      VE_grid_size: [32, 32, 32]
      microstructure_seeds::from_random:
        box_size: [1, 1, 1]
        num_seeds: 2000
        phase_label: Al
      orientations::from_file:
        path: path/to/quaternions.txt
        delimiter: "\t" # however you format .txt
        start_index: 1 # skip header row
        unit_cell_alignment:
          x: a
          y: b
          z: c
        representation:
          type: quaternion
          quat_order: 0 # 0=SCALAR-VECTOR(MTEX:abcd) 1=VECTOR-SCALAR(MTEX:bcda)

[gcapes]

Adam plans to incorporate this into the docs at some point using this example
https://github.com/hpcflow/matflow/blob/develop/matflow/tests/data/define_orientations.yaml