Add badge for Ruff.

Author: jaraco

README.rst

@@ -7,6 +7,10 @@
    :target: https://github.com/PROJECT_PATH/actions?query=workflow%3A%22tests%22
    :alt: tests
 
+.. image:: https://img.shields.io/endpoint?url=https://raw.githubusercontent.com/charliermarsh/ruff/main/assets/badge/v2.json
+    :target: https://github.com/astral-sh/ruff
+    :alt: Ruff
+
 .. image:: https://img.shields.io/badge/code%20style-black-000000.svg
    :target: https://github.com/psf/black
    :alt: Code style: Black