Read README as UTF-8 in setup

[CodingFeng101]

Summary

This makes setup.py read README.md explicitly as UTF-8 before passing it as the package long description.

On Windows systems whose preferred locale encoding is not UTF-8, pip install -e . can fail while setup.py reads the README during editable-build metadata preparation. In my environment the default codec was GBK, and the README contains non-ASCII UTF-8 text, so setup failed before metadata generation completed.

Validation

• Before this change, python -m pip install -e . nose2 flake8 failed with UnicodeDecodeError: 'gbk' codec can't decode byte 0x88 ... while reading README.md from setup.py.
• After this change, python -m pip uninstall -y furl; python -m pip install -e . succeeds and builds the editable wheel.
• python -m flake8 passes.
• git diff --check passes.

I also ran python -m nose2; it currently fails on Python 3.12 with two invalid-bracketed-host ValueErrors and one odd URL assertion in existing URL parsing tests. Those failures are unrelated to this setup.py encoding change.