The slide show for the installation is generated from slideshow.xml by converting all sections to separate rich text files. The files are named according to the section labels. YaST reads them in alphabetical order so it's recommended to name them e.g '01_welcome', '02_whatever', etc. YaST also shows an image alongside the text. The image files in the 'pic/' directory have to be in png format and named according to the section label, ie 01_welcome.png, 02_whatever.png etc.