A proposition to add headings to the list after some time spent in them

I spend a lot of time just searching and scrolling around. I'd like the headers I visit manually to be added to the list after some time.

The quick and dirty way I found is to add a dummy function to the `org-recent-headings-advise-functions` and call it with `run-with-timer` every once in a while. Not the best way, but good enough for now. Here's the code:

```
(use-package org-recent-headings
:config
(defun org-recent-headings-my-aux-fn () nil)
(add-to-list 'org-recent-headings-advise-functions #'org-recent-headings-my-aux-fn)
(let ((repeat-interval 20))
(if (boundp 'org-recent-headings-my-timer)
(cancel-timer org-recent-headings-my-timer))
(setq org-recent-headings-my-timer
(run-with-timer 0 repeat-interval #'org-recent-headings-my-aux-fn))
)
(org-recent-headings-mode) ; this clears the list, unfortunately
)
```

Thanks for the package.