use rich markup for PEP reference (GH-7939)


it's better to refer to PEP with `pep` role in reStructuredText. It also links to the PEP page.
(cherry picked from commit df748c20dabcec5a6e89e0dd74fff21110f8755a)

Co-authored-by: Behzad B. Mokhtari <35877268+perplexionist@users.noreply.github.com>
1 file changed