Issue #23725: Overhaul tempfile docs.

Patch from Zbigniew Jędrzejewski-Szmek.

diff --cc Misc/NEWS
index c2ea6d658db5ba8780afef105dafe43c6e6304ba,81c18d7bff1c193c3fa717980576429be952a2d7..7a5c87ac944e85673d6a1daf0b71f7e28c406a6a
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -84,6 -81,6 +84,9 @@@ Librar
  Documentation
  -------------
  
++- Issue #23725: Overhaul tempfile docs. Note deprecated status of mktemp.
++  Patch from Zbigniew Jędrzejewski-Szmek.
++
  - Issue #24129: Clarify the reference documentation for name resolution.
    This includes removing the assumption that readers will be familiar with the
    name resolution scheme Python used prior to the introduction of lexical