✨ Install pseudo families from string

[mbercx]

Even as the aiida-pseudo maintainer, I just ran:

$ aiida-pseudo install SSSP/1.3/PBEsol/efficiency
Usage: aiida-pseudo install [OPTIONS] COMMAND [ARGS]...
Try 'aiida-pseudo install -h' for help.

Error: `SSSP/1.3/PBEsol/efficiency` is not a install command.

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Obviously, that won't work. But maybe it should? That would be quite intuitive, I'd say, and not too hard to implement.