gh-91279: Note SOURCE_DATE_EPOCH support in ZipFile.writestr() doc (#139396)

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: Wulian233

Doc/library/zipfile.rst

@@ -533,6 +533,11 @@ ZipFile objects
       a closed ZipFile will raise a :exc:`ValueError`.  Previously,
       a :exc:`RuntimeError` was raised.
 
+   .. versionchanged:: 3.14
+      Now respects the :envvar:`SOURCE_DATE_EPOCH` environment variable.
+      If set, it uses this value as the modification timestamp for the file
+      written into the ZIP archive, instead of using the current time.
+
 .. method:: ZipFile.mkdir(zinfo_or_directory, mode=511)
 
    Create a directory inside the archive.  If *zinfo_or_directory* is a string,