Custom .md files in grav admin plugin /pages folder

Hello folks!

I am trying to add custom .md files in user/plugins/admin/pages/admin/ folder. And the question is how to add markdown file which will not be deleted after admin plugin update.

My .md file contains reservations and it is needed to render my reservation.html.twig template. I Have managed to do admin templates override in my custom plugin, but can not figure out how to add files which is edited automaticaly when client places a reservation. And I want these reservations to be visible only in admin panel.

Thanks for help!