The docs are here:

https://github.com/Invisible-Computers/image-gallery/blob/ma...

I admit that this is still a bit rough around the edges...

As a simpler alternative, if you just want to build some layout for yourself and you do not need user management, you can simply render it as an image on the internet and point the device to it:

https://www.invisible-computers.com/invisible-calendar/image...