[doc] Add basic documentation for toml configuration files

Author: Pierre-Sassoulas

doc/user_guide/run.rst

@@ -100,6 +100,9 @@ configuration file in the following order and uses the first one it finds:
 #. ``.pylintrc`` in the current working directory
 #. ``pyproject.toml`` in the current working directory,
    providing it has at least one ``tool.pylint.`` section.
+   The ``pyproject.toml`` must prepend section names with ``tool.pylint.``,
+   for example ``[tool.pylint.'MESSAGES CONTROL']``. They can also be passed
+   in on the command line.
 #. ``setup.cfg`` in the current working directory,
    providing it has at least one ``pylint.`` section
 #. If the current working directory is in a Python package, Pylint searches \