Add content-type for long-description. (#11)

Causes markdown to render correctly on pypi

Signed-off-by: Evan Anderson <[email protected]>

Author: evankanderson

setup.cfg

@@ -3,6 +3,7 @@ name = cloudevents
 summary = CloudEvents SDK Python
 description-file =
     README.md
+long-description-content-type = text/markdown
 author = Denis Makogon
 author-email = [email protected]
 home-page = https://cloudevents.io/