Missing contributor's guide

It would be incredibly helpful if there was any guide for new wallpaper contributions for things such as:

- Desired aspect ratios
- Minimal resolution
- Technical specification (lossless compression, etc.)
- File size

Currently, I feel like the wallpapers are all over the place in terms of size and technical quality. For example, "CachyOS_Moon.jpg" is only 1920x1080 but HEAVILY compressed, to the point where the JPEG artifacts make the entire wallpaper look bad.

It would be much better if this was standardized, so that there was consistent quality among all wallpapers.

**Furthermore**, I believe that quality should be given priority over file size. Most people have at least 500 GB of storage. Even if we assume only 256 GB of storage, then taking up an entire gigabyte for 10-20 lossless high resolution images, that would only be less than half a percent of storage space taken up.

The issue names no files, tests, or entry points. Start by inspecting the repository for any existing contributor or wallpaper documentation and compare the listed wallpaper examples; done means documenting agreed guidance for aspect ratio, resolution, compression, technical quality, and file size.

Written by the indexing model from the issue text.