fix setup.py long_description_content_type (#223)

Author: arun3688

setup.py

@@ -51,6 +51,7 @@ def generateIDL():
       version='3.6.0',
       description='OpenModelica-Python API Interface',
       long_description=open('README.md').read(),
+      long_description_content_type='text/markdown',
       author='Anand Kalaiarasi Ganeson',
       author_email='ganan642@student.liu.se',
       maintainer='Adeel Asghar',