Backport PR #411: add long_description to setup.py

Author: rgbkrk

setup.py

@@ -61,6 +61,8 @@ def run(self):
     version         = version_ns['__version__'],
     packages        = packages,
     description     = 'Jupyter protocol implementation and client libraries',
+    long_description=open('README.md').read(),
+    long_description_content_type='text/markdown',
     author          = 'Jupyter Development Team',
     author_email    = '[email protected]',
     url             = 'https://jupyter.org',