explicitly call our the content type of the description (#397)

Author: scbedd

setup.py

@@ -262,6 +262,7 @@ def build_cmake(self, ext):
     version=version,
     description='AMQP 1.0 Client Library for Python',
     long_description=readme + '\n\n' + history,
+    long_description_content_type="text/x-rst",
     license='MIT License',
     author='Microsoft Corporation',
     author_email='[email protected]',