more documentation in README.md

python/code_quality/black/README.md

@@ -2,8 +2,22 @@
 
 ## Objective
 
-Run the [Black code formatter](https://github.com/psf/black) on your Python code to ensure it
-complies with the coding style guide.
+Run [Black](https://github.com/psf/black) on your Python code to ensure it complies with the coding
+style guide. Black is configured with `--check --diff --quiet` rules.
+
+### Global Configuration of Black
+
+To add configuration to `black` shared with any other usage of black (such as manual run,
+pre-commit, etc), you can use `pyproject.toml` configuration file. Learn more
+about [pyproject](https://pip.pypa.io/en/stable/reference/build-system/pyproject-toml/)
+configuration files.
+
+See this example:
+
+```python
+[tool.black]
+line-length = 100
+```
 
 ## How to use it