[3.13] gh-132971: Update shutil.which() docs (GH-133067) (#133804)

gh-132971: Update shutil.which() docs (GH-133067)
(cherry picked from commit d13d5fd)

Co-authored-by: Kokona <[email protected]>

Author: miss-islington

Doc/library/shutil.rst

@@ -454,6 +454,10 @@ Directory and files operations
    :envvar:`PATH` environment variable is read from :data:`os.environ`,
    falling back to :data:`os.defpath` if it is not set.
 
+   If *cmd* contains a directory component, :func:`!which` only checks the
+   specified path directly and does not search the directories listed in
+   *path* or in the system's :envvar:`PATH` environment variable.
+
    On Windows, the current directory is prepended to the *path* if *mode* does
    not include ``os.X_OK``. When the *mode* does include ``os.X_OK``, the
    Windows API ``NeedCurrentDirectoryForExePathW`` will be consulted to