[3.13] gh-136516: Mention installation artifacts as de-facto resources (GH-136419) (GH-137039)

Files like NUL on windows are, from `importlib.resources` point of
view, an artifact caused by installing to a filesystem directory.
Mention these.
(cherry picked from commit fac4964fdb2ae12969b485de496dd6d064fdbe99)

Co-authored-by: Petr Viktorin <encukou@gmail.com>