[3.13] gh-85583: Add an overview of formatted string literals (f-strings) to ``str`` (GH-132689) (#132767)

gh-85583: Add an overview of formatted string literals (f-strings) to ``str`` (GH-132689)
(cherry picked from commit fee808936fd04e850a62c9610498bbb2360efd31)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>