Fix Unicode error on Windows (Issue #200) (#203)

Fix Unicode error on Windows during setup, while trying to read contents
of README.md.

(Issue #200)

setup.py

@@ -6,7 +6,7 @@ from setuptools import find_packages, setup
 with open(Path(__file__).absolute().parents[0] / "langchain" / "VERSION") as _f:
     __version__ = _f.read().strip()
 
-with open("README.md", "r") as f:
+with open("README.md", "r", encoding="utf-8") as f:
     long_description = f.read()
 
 LLM_DEPENDENCIES = ["cohere", "openai", "nlpcloud", "huggingface_hub"]