Clarify pyproject.toml configuration (#63)

Add info on the assumed configuration section and the fact that the `toml` library needs to be installed.

Co-authored-by: Sorin Sbarnea <[email protected]>

Author: felix-hilden

README.rst

@@ -101,7 +101,7 @@ instead.
 * ``$CWD/tox.ini``
 * ``$CWD/pep8.ini``
 * ``$CWD/setup.cfg``
-* ``$CWD/pyproject.toml``
+* ``$CWD/pyproject.toml`` in section ``[tool.doc8]`` if ``toml`` is installed
 
 An example section that can be placed into one of these files::