add unity doc.

unity/XR_RM_PICO_UDP_Sender/README.md

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+# XR-RM PICO UDP Sender
+
+Minimal Unity project for the direct PICO 4 Ultra UDP route in
+`docs/pico4_ultra_udp_teleop_setup.md`.
+
+Configured target:
+
+```text
+Host = 192.168.9.99
+Port = 15000
+Send Hz = 60
+Convert Unity To Project Coordinates = true
+Package Name = com.local.xr_rm_udp_sender
+```
+
+Open this folder with the Ubuntu editor installed at:
+
+```text
+/home/robot/Unity/Hub/Editor/2022.3.62f3c1/Editor/Unity
+```
+
+Install Android Build Support, Android SDK/NDK, and OpenJDK from Unity Hub.
+
+The PICO SDK is referenced from the sibling folder:
+
+```text
+../PICO-Unity-Integration-SDK-release_3.4.0
+```
+
+After opening the project:
+
+1. Wait for Unity Package Manager to import `PICO Integration 3.4.0`.
+2. Run `XR-RM -> Apply UDP Sender Android Settings`.
+3. Build with `XR-RM -> Build Android APK`, or use Unity's Android Build window.
+
+The automated setup enables Android, PICO XR Loader, API 29, Internet access,
+IL2CPP + ARM64, and the `PicoControllerUdpSender` scene object.
+
+Runtime scene components:
+
+- `PicoControllerUdpSender`: sends left/right controller JSON to the ROS2 host.
+- `PicoUdpConfigPanel`: in-headset config panel plus run HUD.
+- `PicoKeepAwake`: while UDP sending is on, requests PICO Enterprise wake lock,
+  disables PICO auto sleep, applies Android `KEEP_SCREEN_ON`, and restores
+  captured screen/sleep timeouts when sending stops.
+
+The setup menu chooses the UDP target host from `XR_RM_UDP_TARGET_HOST` when
+set. Otherwise it auto-detects a local IPv4 address; on this Ubuntu machine the
+current Wi-Fi address is `192.168.9.99`.
+
+Batchmode build example:
+
+```bash
+cd /home/robot/WS_xr/src
+XR_RM_UDP_TARGET_HOST=192.168.9.99 \
+/home/robot/Unity/Hub/Editor/2022.3.62f3c1/Editor/Unity \
+  -batchmode \
+  -quit \
+  -projectPath "$(pwd)/unity/XR_RM_PICO_UDP_Sender" \
+  -executeMethod XrRmUdpSenderProjectSetup.BuildAndroidApk \
+  -logFile "$(pwd)/unity_build.log"
+```