[doc] Add a rational for pylint's default value (#10534)

Due to popular demand. 

PEP8:

> Some teams strongly prefer a longer line length. For code maintained exclusively or primarily by a team that can reach agreement on this issue, it is okay to increase the line length limit up to 99 characters, provided that comments and docstrings are still wrapped at 72 characters.

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

Author: Copilot

.github/copilot-instructions.md

@@ -191,6 +191,8 @@ script/                   # Development utility scripts
 - `.pre-commit-config.yaml` -- Code quality checks configuration
 - `pylintrc` -- Pylint's own configuration
 - `requirements_test_min.txt` -- Minimal test dependencies
+- `.gitignore` do not add the 'venv' inside the .gitignore, don't commit the venv in the
+  first place (humans add it to their global gitignore)
 
 ## Creating New Checkers
 

doc/user_guide/configuration/all-options.rst

@@ -902,7 +902,7 @@ Standard Checkers
 
 --max-line-length
 """""""""""""""""
-*Maximum number of characters on a single line.*
+*Maximum number of characters on a single line. Pylint's default of 100 is based on PEP 8's guidance that teams may choose line lengths up to 99 characters.*
 
 **Default:**  ``100``
 

pylint/checkers/format.py

@@ -166,7 +166,11 @@ class FormatChecker(BaseTokenChecker, BaseRawFileChecker):
                 "default": 100,
                 "type": "int",
                 "metavar": "<int>",
-                "help": "Maximum number of characters on a single line.",
+                "help": (
+                    "Maximum number of characters on a single line. "
+                    "Pylint's default of 100 is based on PEP 8's guidance that teams "
+                    "may choose line lengths up to 99 characters."
+                ),
             },
         ),
         (