docs: flesh out README

README.md

@@ -1,2 +1,20 @@
 # arduino
-Arduino projects
+
+Collection of small Arduino projects and sketches.
+
+## Contents
+
+| Sketch | Description |
+|--------|-------------|
+| `ino/blue_bot.ino` | Bluetooth-controlled robot |
+| `ino/blue_car.ino` | Bluetooth-controlled car |
+| `ino/door_lock.ino` | Door lock controller |
+| `ino/ds_board.ino` | DS sensor board |
+| `ino/ds_kit.ino` | DS sensor kit |
+| `ino/i2c_scanner.ino` | I2C device scanner |
+
+Open any `.ino` file in the [Arduino IDE](https://www.arduino.cc/en/software) to compile and upload.
+
+## License
+
+Apache-2.0 — see [LICENSE](LICENSE).