doc: Update run instructions for Windows (#3563)

Command must run as Administrator, or it fails:

33.506 s   Starting...←[2m2024-12-14T02:18:18.280545Z←[0m ←[33m WARN←[0m ←[2mllama_cpp_server::supervisor←[0m←[2m:←[0m ←[2mcrates\llama-cpp-server\src\supervisor.rs←[0m←[2m:←[0m←[2m98:←[0m llama-server <embedding> exited with status code -1073741515, args: `Command { std: "C:\\tabby_x86_64-windows-msvc-cuda122\\llama-server.exe" "-m" "C:\\Users\\user1\\.tabby\\models\\TabbyML\\Nomic-Embed-Text\\ggml\\model-00001-of-00001.gguf" "--cont-batching" "--port" "30888" "-np" "1" "--log-disable" "--ctx-size" "4096" "-ngl" "9999" "--embedding" "--ubatch-size" "4096", kill_on_drop: true }`

website/docs/quick-start/installation/windows/index.mdx

@@ -34,7 +34,7 @@ nvcc --version
 * In this directory, you'll find an executable file named `tabby.exe`.
 
 ## Running Tabby
-Open a command prompt or PowerShell window in the directory where the `tabby.exe` is located (from the previous step).
+Open a command prompt or PowerShell window, as administrator, in the directory where the `tabby.exe` is located (from the previous step).
 
 Run the following command:
 ```
@@ -48,4 +48,4 @@ Run the following command:
 You should see a success message similar to the one in the screenshot below. After that, you can visit http://localhost:8080 to access your Tabby instance.
 <div align="left">
   <img src={successImage} alt="Windows running success" style={{ width: 800 }} />
-</div>
+</div>