docs(wasi-nn): add BitNet backend

[Khushmagrawal]

Explanation

I am working on adding support for BitNet (WasmEdge/WasmEdge#4161).
This PR adds documentation for building BitNet plugin.
Blocked by: WasmEdge/WasmEdge#4253

Related issue

WasmEdge/WasmEdge#4161

What type of PR is this

/kind documentation

[juntao]

Hello, I am a PR summary agent on flows.network. Here are my reviews of code commits in this PR.

---

Commit 0c6e8dabcf5d5887bd4c3f7c21233ae780545972

Key Changes in the Pull Request

The pull request adds support for a new backend called BitNet within the WASI-NN framework. This backend is compatible with the Microsoft's BitNet library, which is a lightweight neural network library designed for embedding on embedded systems and mobile devices.

The changes include:

1. Adding a New Backend Option: A new backend option BitNet is added to the wasi_nn.md documentation.
2. Backend Configuration: The backend is configured with specific flags (-DWASMEDGE_PLUGIN_WASI_NN_BACKEND="BitNet").
3. Build Instructions: Build instructions for both ARM and x86 architectures with different TL optimization flags are provided.

Additional Considerations

• TL1 Optimization for ARM: Enabling this flag builds the WasmEdge binary optimized specifically for ARM architecture, which can be beneficial on smaller devices.
• TL2 Optimization for x86: This flag provides better performance but might not be necessary for all use cases.
• Cross-Platform Compatibility: The inclusion of BitNet backend allows WasmEdge to support a wider range of neural network models and architectures beyond the existing backends.

These updates enhance the capabilities of WasmEdge by adding new features and optimizations, making it more versatile in different applications.