The simple multi-buffer material set example in the docs is ambiguous

[JustinPrivitera]

https://llnl-conduit.readthedocs.io/en/latest/blueprint_mesh.html#multi-buffer-material-sets

There is no way to map the volume fractions back to the elements. The indices for array a are ambiguous.

Excluding sizes and offsets implies that sizes are all 1 and offsets are increasing by 1 each index. Indices should have the same number of elements.