add data files as SNOSHEWS.data submodule?

[JostMigenda]

The repo includes two sample files (profiles00585_stp.d and profiles00585_Ye.d) which are hard-coded in SNOSHEWS_example.py; so the user has to manually download them and ensure they are in the current working directory.

Unlike in BEMEWS (where the same PREM data files will be used everytime), these data files will need to be different for each progenitor, so users will generally need to provide their own data files. I wonder if it would still be nice to include those files as a submodule[*] to make it easier to run the demo script? Definitely not a high priority, though; we’ve got some more important work to do to get snewpy v2.0, EMEWS and SNOSHEWS out to users first.

[*] I.e. add them to the installable package (sdist or wheel), so users automatically get them when they run pip install. We would then be able to access the files via importlib.resources, similar to the SNOwGLoBES data files.