Word shell mention of shlex.split more carefully

To avert the mistake of not removing `shell=True` when using it.

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: EliahKagan

git/cmd.py

@@ -1222,7 +1222,8 @@ def execute(
 
             On Unix-like systems, when migrating away from passing string commands with
             ``shell=True``, :func:`shlex.split` may serve as a transitional step in rare
-            cases, but this should be undertaken with extreme care. See the `command`
+            cases, but this should be undertaken with extreme care, and the resulting
+            sequence should then be passed with ``shell=False``. See the `command`
             parameter above on the risks.
 
         :param env: