Mention in What's New for 3.15

Author: clin1234

Doc/whatsnew/3.15.rst

@@ -823,6 +823,7 @@ mimetypes
   (Contributed by John Franey in :gh:`140937`.)
 * Add ``application/toml``. (Contributed by Gil Forcada in :gh:`139959`.)
 * Add ``image/jxl``. (Contributed by Foolbar in :gh:`144213`.)
+* Add ``application/efi``. (Contributed by Charlie Lin in :gh:`145720`.)
 * Rename ``application/x-texinfo`` to ``application/texinfo``.
   (Contributed by Charlie Lin in :gh:`140165`.)
 * Changed the MIME type for ``.ai`` files to ``application/pdf``.