This didn't work for me, I can't seem to get the slideshow feature to work with the latest version of customloadingscreen.

Temporary instructions, I'll update these when it's been tested to work a bit:

1. Download Custom Loading Screen 0.5.0-pre.1 for 1.12.2
2. In config/customloadingscreen.cfg Change S:screen_config to S:screen_config=sample/slideshow
3. Create a folder config/customloadingscreen/
4. Add your slideshow images in config/customloadingscreen/ named slideshow_1.png, slideshow_2.png, slideshow_3.png, etc

Additional instructions, if you want to tweak the slideshow itself:

1. Download Custom Loading Screen 1.5.1 for 1.12.2
2. In config/customloadingscreen.cfg Change S:screen_config to S:screen_config=config/slideshow
3. Create a folder config/customloadingscreen/
4. Add your slideshow images in config/customloadingscreen/ named slideshow_1.png, slideshow_2.png, slideshow_3.png, etc
5. Copy the contents of this file into a new file in config/customloadingscreen/slideshow.json.
6. Change any of the 4 constants at the top of the file to tweak the slideshow a little bit.