Set long_description_content_type in setup.py

This means that pypi renders the README correctly

Author: inclement

setup.py

@@ -86,6 +86,7 @@ def recursively_include(results, directory, patterns):
       version=version,
       description='Android APK packager for Python scripts and apps',
       long_description=long_description,
+      long_description_content_type='text/markdown',
       author='The Kivy team',
       author_email='kivy-dev@googlegroups.com',
       url='https://github.com/kivy/python-for-android',