create a test or few that will run a diffpy.cmi script in CI

[sbillinge]

This will let us see whether things are passing on conda-forge when we create the feedstock

can we steal these tests from diffpy.srreal and/or diffpy.srfit? Or we could grab scripts from pdfitc and set them up to run as tests. Or both in the long run (fewer tests for this first release, more later)?

[cadenmyers13]

Assigned to @Tieqiong