Include license information in setup.py (#170)

Author: maffoo

setup.py

@@ -143,6 +143,7 @@ def build_extension(self, ext):
     description="A package for decoding quantum error correcting codes using minimum-weight perfect matching.",
     long_description=long_description,
     long_description_content_type='text/markdown',
+    license="Apache 2",
     ext_modules=[CMakeExtension("pymatching._cpp_pymatching")],
     packages=find_packages("src"),
     package_dir={'': 'src'},