docs: flesh out README

README.md

@@ -1,2 +1,15 @@
 # time-changer
-A tool to easy change Windows system time
+
+Small Go tool to easily change the Windows system time from the command line.
+
+## Quick start
+
+```bash
+go build -o time-changer.exe .
+# Run as Administrator:
+time-changer.exe "2025-01-15 08:30:00"
+```
+
+## License
+
+Apache-2.0 — see [LICENSE](LICENSE).