With the introduction of sparql harvesting the need for instructions on how to consume the "unused images" reports has become more obvious. See e.g.

In T174333#3587569, @Effeietsanders wrote:

@Lokal_Profil I'm not sure if after that the workflow of adding images to the items is entirely clear. You may want to put those instructions on top of those pages (this is different for Wikidata than wikipedia-lists).

Since the pages are published on different wikis (in different languages) a template is not possible. Instead the best solution is a documentation page on commons together with a mechanism for embedding localised instructions on the page.

This can be done by:

• changing the top of the generated reports to {{#ifexist:{{FULLPAGENAME}}/header | {{/header}} |For information on how to use this report and how to localise these instructions visit [[:c:Commons:Monuments database/Unused images]]. }} (i.e. adding a default text when no header exists).
• update Commons:Monuments database/Unused images to have explain that:
  • the /header subpage can be used for localised instructions
  • how to add images on Wikidata and generically how to do this on lists
  • move/remove updated or unnecessary information

The /header solution additionally provides a way for wikis to categorise the report pages if they wish and a similar structure could be used for the other generated reports.