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…
README is usually a text file. While some platforms can now use markdown, that is nowhere near universal. So it might be better to ask for screenshots to be put on the website / wiki.
GitHub and GitLab both support inserting images into your README.md. Here’s the syntax:
Just like obsidian.md
And anything that supports CommonMark. It’s even in the original Markdown
Not just a text file, a markdown file. And markdown has supported images since forever
README.txt will be a text file, README.md can be much more