MNT: Use utf-8 encoding when reading README.rst

Avoid UnicodeDecodeErrors on some platforms that default to ascii encoding and fail to read the non-ascii characters.

setup.py

@@ -9,7 +9,7 @@
 from setuptools import setup
 
 here = os.path.abspath(os.path.dirname(__file__))
-with open(os.path.join(here, 'README.rst')) as fd:
+with open(os.path.join(here, 'README.rst'), encoding='utf-8') as fd:
     long_description = fd.read()