Improve ansible.builtin.copy directory_mode parameter docs (#81127)

* Improve ansible.builtin.copy directory_mode parameter docs

lib/ansible/modules/copy.py

@@ -79,9 +79,10 @@ options:
       See CVE-2020-1736 for further details.
   directory_mode:
     description:
-    - When doing a recursive copy set the mode for the directories.
+    - Set the access permissions of newly created directories to the given mode.
-    - If this is not set we will use the system defaults.
+      Permissions on existing directories do not change.
-    - The mode is only set on directories which are newly created, and will not affect those that already existed.
+    - See C(mode) for the syntax of accepted values.
+    - The target system's defaults determine permissions when this parameter is not set.
     type: raw
     version_added: '1.5'
   remote_src: