Open source devs: please, please add screenshots...
I beg you, if you are a developer of an open source app or program - add screenshots of your app to the README file.
When looking for the perfect app, I had to install dozens of them just to see what the user interface looked like and whether it suits me.
This will allow users to decide if the app they choose will suit them...
Please, don't think about it, just do it....
While I get the sentiment, historically, readmes have been text only, and should predominately focus on usage options, not a sales pitch. Today in GitHub, these files support markdown, but the level of effort is probably two orders of magnitude higher than a text readme alone.
Think of a readme file on GitHub/distributed with the binary more as a man page than a proper website.
I mean, yes, it's a little more effort, but I think you're over playing how much effort is required. Writing a half decent readme is vastly easier than frankly any feature or bug fix. Taking a couple of notable screenshots is super easy. Writing docs is hard (I've written tons for large and complicated projects), but readmes are the easiest and including screenshots is really quite easy.
Everywhere supports markdown in readmes now. Literally everywhere I've ever hosted code. And markdown with links to images is perfectly fine even if viewed in plain text mode. They'll just click the link and view the image standalone. I've done that plenty of times, too. Every editor (plus in-browser code hosts in plain text mode) makes it easy.