[Docs] ggml: add README for the embedding example with CI job

[dm4]

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[juntao]

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

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Commit 18a8d056d3135a028d30cdb69c2f01c2f06fa2f1

Key Changes:

1. Added a new README.md file for the embedding example in the wasmedge-ggml/embedding directory.
2. Updated the llama.yml workflow file to include a new job named "Embedding Example" that builds and runs the embedding example using the GGML backend.
3. The embedding example job now includes commands to download a model, build the project, and run the WASM binary with the specified model for generating embeddings.
4. The README includes instructions on downloading the model, parameters, and execution steps, along with sample output for interacting with the embeddings.

Potential Problems:

1. The README mentions referencing the wasmedge-ggml/README.md file for general introductions and setup. Ensure that the links are accurate and lead to the correct locations.
2. The new job was added to the llama.yml file without removing the previously existing "Build embedding" job. This redundancy should be addressed to avoid confusion or unnecessary build processes.
3. It's important to ensure that the commands added for the embedding example are functioning correctly and do not introduce errors in the build or execution process.
4. The README and the job description should be reviewed for clarity and completeness. Users should be able to follow the instructions easily and understand the purpose of the embedding example.