Document Python 2 deprecation (#6910)


diff --git a/setup.py b/setup.py
index 578e142..847d6ed 100644
--- a/setup.py
+++ b/setup.py
@@ -93,6 +93,7 @@
     namespace_packages=namespaces,
     install_requires=dependencies,
     extras_require=extras,
+    python_requires='>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*',
     include_package_data=True,
     zip_safe=False,
 )