Allow this to be installed with modern setuptools.

[btimby]

When installing this library, you can receive the following error:

#12 19.22 "/tmp/pip-build-env-s4if5gvs/overlay/lib/python3.13/site-packages/setuptools/dis
#12 19.22 t.py", line 629, in _enforce_underscore
#12 19.22           raise InvalidConfigError(
#12 19.22           ...<3 lines>...
#12 19.22           )
#12 19.22       setuptools.errors.InvalidConfigError: Invalid dash-separated key 
#12 19.22 'description-file' in 'metadata' (setup.cfg), please use the underscore name 
#12 19.22 'description_file' instead.

This syntax has been deprecated, and finally removed. This PR resolves the syntax error.