Most people don't do the smart thing you did.... put screenshots in the readme.
For a GUI program, it's a MUST in my opinion. I mean, you've built something that's visual so a picture is the way to go.
I should rework the date chooser window using a PySimpleGUI built-window instead of the tkinter based one that I integrated in long ago. I've seen some people build their own calendar right into the main window itself.
Thanks for giving PySimpleGUI a shot and thanks for the Tweet!! Congrats on making a nice looking application.