Where to draw the line for authorship for a software-announcement paper?
As the discussion underneath this post shows, there is no set of established guidelines within a single subfield, let alone across all academia, as to where to draw the line.

A different, not unrelated question: what are you trying to achieve with this paper?

If it's about trying to properly apportion credit for the work done in producing the software, then this is a hard problem: there's the work of the FORCE11 Software Citation Group and their paper. But as the software grows and changes, you're going to have to keep making these decisions.

If it's about growing a community around the software, to improve it, get more people to use it and contribute, then there's a thoughtful post here. That's about much more than just a paper, but notes many problems with giving the proper credit when a software project is updated and the members of the community change.

My opinion, for what it's worth: the more broadly you extend authorship invitations, and the more broadly you're seen to do so, the more likely you are to get community buy-in and future support. By making clear expectations about concrete contributions to the paper-writing process itself, you may reduce conflicts around the free-rider problem.