Explicitly mention supported Python versions in setup.py
diff --git a/setup.py b/setup.py
index 428b14c..1ec0268 100755
--- a/setup.py
+++ b/setup.py
@@ -35,7 +35,13 @@
               'License :: OSI Approved :: Apache Software License',
               'Operating System :: OS Independent',
               'Programming Language :: Python',
+              'Programming Language :: Python :: 2',
+              'Programming Language :: Python :: 2.6',
+              'Programming Language :: Python :: 2.7',
               'Programming Language :: Python :: 3',
+              'Programming Language :: Python :: 3.3',
+              'Programming Language :: Python :: 3.4',
+              'Programming Language :: Python :: 3.5',
               'Topic :: Security :: Cryptography',
           ],
           install_requires=[