Fix README.md in setup.py

Author: skybber

setup.py

@@ -4,7 +4,7 @@
 from udger import __version__
 
 
-with open(join(dirname(__file__), 'README.rst')) as readme_file:
+with open(join(dirname(__file__), 'README.md')) as readme_file:
     long_description = readme_file.read()