Because open source projects are usually developed by a community of contributors, it might be better to talk with some of those communities. That way you have

Because open source projects are usually developed by a community of contributors, it might be better to talk with some of those communities. That way you have access to the reasons existing documentation is the way it is. Sure, it might be more work than soliciting user complaints. But opining “your documentation is bad” is unlikely to foster the conditions that actually improve actual documentation for actual projects. Documentation problems are usually the result of effort writing documentation by people highly technically informed about a project, tooling is rounding error. Good luck.