docs: document non-root GPU access for Turnip

Add a note to the Turnip section (EN and zh-CN) explaining that non-root
users must be added to the droidspaces-gpu group to access the GPU device
nodes.

Signed-off-by: ravindu644 <droidcasts@protonmail.com>

Author: ravindu644

Documentation/Graphics-and-Audio.md

@@ -164,6 +164,10 @@ Near-native hardware acceleration for **Qualcomm Adreno GPUs** using the open-so
 
 4. Run a GUI application inside the container - Turnip GPU acceleration will be active.
 
+> [!NOTE]
+>
+> **Permission Management (Non-Root Users):** If you are using a non-root user, you must grant them access to the GPU device nodes: `sudo usermod -aG droidspaces-gpu <your_username>`
+
 ---
 
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Documentation/zh-CN/Graphics-and-Audio.md

@@ -164,6 +164,11 @@ Droidspaces 会自动启动 X 服务器和 VirGL 服务器，并将 `DISPLAY=:5`
 
 4. 在容器内运行 GUI 程序 — Turnip GPU 加速将自动生效。
 
+> [!NOTE]
+>
+> **权限管理（非 root 用户）：** 如果你使用的是非 root 用户，则必须授予其访问 GPU 设备节点的权限：
+`sudo usermod -aG droidspaces-gpu <your_username>`
+
 ---
 
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