Check velocity transposes in docs

[FredDeCeuster]

Potential issue with velocity transposes in docs.
https://magritte.readthedocs.io/en/stable/1_examples/1_post-processing/1_create_AMRVAC_3D.html#Extract-data

[ThomasCeulemans]

After checking, I do not think there is anything wrong with the velocity field. I have respectively plotted the slices of the x, y and z components of the velocity fields below (units: fraction of speed of light). The x-component nicely divides the model into two parts around x=0; the y component does the same at y=0, and the z-component is small (due to being at z=0. As we expect a spherically symmetric wind when no perturbers are present, the velocity field seems fine to me.