chore: improve documentation around pyproject.toml usage

Author: rubik

README.rst

@@ -58,7 +58,8 @@ With Pip:
 
     $ pip install radon
 
-With Pip and `pyproject.toml` support on Python <3.11:
+If you want to configure Radon from `pyproject.toml` and you run Python <3.11,
+you'll need the extra `toml` dependency:
 
 .. code-block:: sh
 

docs/commandline.rst

@@ -23,7 +23,7 @@ For example, all of the radon commands have a ``--exclude`` and ``--ignore`` arg
 Radon will look for the following files to determine default arguments:
 
 * ``radon.cfg``
-* ``pyproject.toml`` (with optional toml install before python 3.11)
+* ``pyproject.toml`` (with optional `toml` install on Python <3.11)
 * ``setup.cfg``
 * ``~/.radon.cfg``