Silence checkdoc messages about docstrings of internal objects

Internal objects here don’t have and shouldn’t have documentation
strings because:

- There is nothing useful to specify in them.
- They are not a stable API to be used.
- They would pollute the source file and make it larger.

pip-frame.el

@@ -233,4 +233,8 @@ Any other key stops this command and executes its own command."
 
 (provide 'pip-frame)
 
+;; Local Variables:
+;; checkdoc-force-docstrings-flag: nil
+;; End:
+
 ;;; pip-frame.el ends here