Scaffold Java 21 multi-module project with UMD ISO + SFO parsing

- Gradle Kotlin DSL multi-module (core, ui, cli) with JPMS modules
- UMD ISO 9660 reader (UmdIsoReader/UmdIsoFile + sector devices)
- SFO (param.sfo) parser
- 'dump' CLI command: metadata + recursive file listing
- JUnit 5 + AssertJ tests (SFO and ISO reader)
- Switch license from MIT to GPL-3.0-or-later

README.md

@@ -1,3 +1,28 @@
 # useless-umd-player
 
-umd video player to enjoy limited dvd menus in 720x480 pixels
+umd video player to enjoy limited dvd menus in 720x480 pixels
+
+A standalone player for PSP UMD Video ISO images: open a disc, render its real
+menu, and play the movie (H.264 video + ATRAC3+ audio) with mouse and
+keyboard/media-key controls.
+
+> **Status:** early development. Currently implemented: ISO 9660/UMD reading,
+> `param.sfo` metadata parsing, and file listing.
+
+## Build
+
+Requires JDK 21 (Gradle auto-provisions it via the Foojay toolchain resolver).
+
+```sh
+./gradlew build
+```
+
+## Run
+
+```sh
+./gradlew cli:run --args="dump /path/to/disc.iso"
+```
+
+## License
+
+GPL-3.0-or-later — see [LICENSE](LICENSE).