To be honest, not yours. I'm immediately suspicious of "open source" projects written by OS X/iOS users and demonstrated on said platforms. Without installing your program myself, I can't expect it to work on GNU/Linux, since all of your screenshots are taken in Safari.
Thanks for the feedback - I'm curious if you have any suggestions for how I can assure you that it will work on GNU/Linux? The second sentence of the installation instructions links to "setup instructions for a Linux-based VPS".
If you really want to broaden appeal you should do what Dropbox does on their download page – show screenshots specific to the user's OS. If your serve the images embedded into GitHub README from your own hosting, you can do that very easily. But you'll have to take all these screenshots, no way around that.
Just taking your screenshots from Iceweasel/Chromium instead of Safari would be an easy step. It shows that you've tried your project on a GNU/Linux platform at least once. I don't use any Webkit-based browsers, so it doesn't help me at all if you've designed your site/project to work well with Webkit.
So perhaps you should keep doing what you are doing and not get derailed by someone whose goal is not to find a good software, but is to gripe about the marginalization of Linux even when it is completely irrelevant to context.
No, I would say showing screenshots from all "supported" platforms is a good idea. The cost is very low, and preventing people from feeling marginalized is a win for you and your software.
Anecdotally, I can say that I am going to have a look at the software, and this just because the author was willing to consider us Linux users.
To be honest, not yours. I'm immediately suspicious of "open source" projects written by OS X/iOS users and demonstrated on said platforms. Without installing your program myself, I can't expect it to work on GNU/Linux, since all of your screenshots are taken in Safari.