📝 Improve the note about editable installs

Co-Authored-By: Paul Ganssle <pganssle@users.noreply.github.com>

docs/setuptools.txt

@@ -2207,7 +2207,7 @@ only a ``setuptools.setup()`` call.
 .. note::
 
     :pep:`517` doesn't support editable installs so this is currently
-    incompatible with ``pip install -e .``.
+    incompatible with ``pip install -e .``, as :pep:`517` does not support editable installs.
 
 This means that you can have a Python project with all build configuration
 specified in ``setup.cfg``, without a ``setup.py`` file, if you **can rely