Notice text on public sharing page

Hello community!

Nextcloud works fine on my server but I have got one little question. How is it possible to show the expiration date on public sharing webpage? I would like to set a notice text at the bottom or on the top of the webpage like “This share will expire on 2017-05-31”.

I have got no trouble to edit html or php files but I cannot find the corresponding files to do that.

Thanks a lot!