Explicitly declare the package in setup.py

Setuptools recently added automatic discovery of packages and namespaces
within given source trees/projects, however isrcsubmit’s current layout
does not play well with this autodiscovery.

Explicitly declaring which Python package is being touched by using this
setup.py is probably the easiest and quickest way to remedy this.
We may want to switch to another solution down the line, but this should
work okay for the time being.

See https://setuptools.pypa.io/en/latest/userguide/package_discovery.html
for more details.

Fixes JonnyJD#140

setup.py

@@ -102,6 +102,7 @@ def run(self):
         url="https://github.com/JonnyJD/musicbrainz-isrcsubmit",
         requires=["discid(>=1.0.0)", "musicbrainzngs(>=0.4)"],
         python_requires='>=3.7',
+        packages=["isrcsubmit"],
         scripts=["isrcsubmit.py"],
         license="GPLv3+",
         classifiers=[