add mtp develop guide doc

[zouyida2052]

What this PR does / why we need it?

add mtp develop guide doc

Does this PR introduce any user-facing change?

no

How was this patch tested?

[github-actions]

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[gemini-code-assist]

Code Review

This pull request adds a developer guide for Multi-Token Prediction (MTP). The documentation is well-structured and provides a good overview of the feature, its usage, and implementation details. I've found a minor but important typo in a command-line example that could cause issues for users. Correcting this will improve the quality of the documentation.

[gemini-code-assist]

There is a typo in the example command. A trailing single quote ' is present, which will cause a shell error if a user copy-pastes it. Please remove it to ensure the command is correct.

Suggested change

	`--speculative_config={"method": "deepseek_mtp", "num_speculative_tokens": 1}'`
	`--speculative_config={"method": "deepseek_mtp", "num_speculative_tokens": 1}`

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[wangxiyuan]

we'll cherry-pick docs from main in one PR later. Thanks.