docs: flesh out README

target/README.md

@@ -1,2 +1,15 @@
 # time-mocker-target
-Java application target to test [time-mocker](https://github.com/tiennm99/time-mocker)
+
+Java test target for [time-mocker](https://github.com/tiennm99/time-mocker) — validates injected fake time behavior.
+
+## Quick start
+
+```bash
+./gradlew run
+```
+
+Run alongside `time-mocker` to verify that system time injection works correctly.
+
+## License
+
+Apache-2.0 — see [LICENSE](LICENSE).