Add sample dockerfile

[lynzrand]

No description provided.

[peter-jerry-ye-code-review]

From the provided git diff output, it appears that a new Dockerfile for MoonBit has been created. Here are some observations and suggestions based on the changes:

1. Missing Example Implementation: The comment # No example implementation provided in public repository suggests that the example implementation is not included in the public repository. This might be intentional, but it's worth noting that users might expect some example code to be present to understand how to use the MoonBit toolchain. Consider adding a simple example or documentation on how to get started with MoonBit.

2. Environment Variables and Path Management: The Dockerfile sets up the environment by adding several directories to the PATH variable. This is crucial for ensuring that all necessary tools are accessible. However, it's important to verify that there are no conflicts or redundancies in the paths added. Additionally, consider documenting these environment variables and paths in the README or a setup guide for clarity.

3. Dependency Installation: The Dockerfile installs several dependencies and tools, including nodejs, zig, wasm-tools, and libriscv. Ensure that the versions specified are compatible with each other and with the MoonBit toolchain. For instance, the moon update command should be executed after installing the MoonBit toolchain to ensure it's up-to-date. Regularly review and update these dependencies as necessary to avoid compatibility issues.

These suggestions aim to enhance the Dockerfile and the setup process for users who will be building and running MoonBit applications.