Updated setup.py for README.rst support instead of README.md.

setup.py

@@ -9,7 +9,7 @@ with open("sen2chain/__init__.py", encoding="utf-8") as f:
         if line.startswith("__version__"):
             version = line.split("=")[1].strip().strip("\"")
 
-with open(path.join(here, "README.md"), encoding="utf-8") as f:
+with open(path.join(here, "README.rst"), encoding="utf-8") as f:
     long_description = f.read()
 
 setup(