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…
Where: In the repository, most projects seem to use media or screenshots as the name of the directory.
How often: Whenever a big change happened or many small changes have accumulated.
What: Light theme suffices. I only care about the general look and feel, not about specific colors.
That’s how I would do it for my own projects.
As an example, an old Android project of mine: https://github.com/moritzruth/JamRSS
I showed one screen in both the light and the dark variant to demonstrate that the app generally has support for dark mode.
