@cra a link to pagure docs is doable. As for "how to become a co-maintainer", do you mean the whole process, or just the pagure specific bits?

The process is to contact the maintainer and ask to be a co-maintainer, at which point the maintainer gives the necessary access.

it's covered here for new-comers, for example, but the expectation is that packagers know how to go about this:
https://docs.fedoraproject.org/en-US/package-maintainers/How_to_Get_Sponsored_into_the_Packager_Group/#become_a_co_maintainer

Would be be open to opening a pull request with the changes you think are necessary please?

I looked around the documentation a bit from this perspective.
It is true that the instructions regarding how to add a co-maintainer are well hidden.
The path to them is as follows:

1. Page Joining the Package Maintainers
2. Section Understand your responsibilities
3. Follow link Policy for Encouraging Comaintainers of Packages
4. Last section Procedure takes you to the instructions in a wiki page

I was considering adding a page How to add a co-maintainer,
which would basically just link to that policy,
perhaps also to Pagure's own documentation and the wiki instructions.
But I did not do that yet, because there so little so say about that topic.

A larger topic surfaces here once again:
The relationship between Package Maintainer Docs and FESCo policies.
Quite a lot of material that was once part of the Packager Maintainers wiki category
has been migrated to FESCo policies, where they belong.
The problem is that often package maintainers look of material in the Package Maintainer Docs,
but it is actually covered by a FESCo policy.
This is a case here, too.
(With the twist that perhaps the FESCo policy should not bother with how this is implemented in Pagure).
I submitted #80 to promote the FESCo docs better in the index page.
That should help a little bit.

A pull request with something even better is still welcome,
if somebody is willing to contribute.