Add README.md and change image name

README.md

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+# Skins image
+
+A lightweight Docker image for running Danser (danser-go) on Ubuntu 25.10, complete with FFmpeg, ImageMagick, Node.js, and necessary fonts & libraries. 
+
+Used for all the Actions to generate Skins.
+
+## Features
+
+* **Base**: Ubuntu 25.10
+* **Danser-go**: Automatically downloads the latest Linux build of [Wieku/danser-go](https://github.com/Wieku/danser-go)
+* **FFmpeg**: Latest GPL shared build for video processing (Nvidia Support)
+* **ImageMagick**: Compiled from source with support for common image formats and fonts
+* **Node.js**: Version 20.x and latest npm for any scripting needs
+* **Dependencies**: Xvfb, GTK, Ghostscript, Git LFS, font packages, and more
+* **Preloaded Content**: Sample beatmap `297969n.osz` (Caramel Heaven) and default settings
+
+## Directory Structure
+
+```
+/app/danser/
+├── songs/           # .osz files (beatmaps) and extracted folders
+├── settings/        # Danser configuration JSON files
+├── videos/          # Generated videos
+├── ffmpeg/          # FFmpeg binaries
+└── screenshots/     # Captured screenshots
+
+```