Add supported OS's

Fixes #37

Author: carver

setup.py

@@ -69,6 +69,8 @@
         'Intended Audience :: Developers',
         'License :: OSI Approved :: MIT License',
         'Natural Language :: English',
+        'Operating System :: MacOS',
+        'Operating System :: POSIX',
         'Programming Language :: Python :: 3',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',