docs: Add documentation for Wan 2.2 Animate pipeline

[mathieu-thomas]

This commit adds a new documentation file, docs/WAN_2.2_ANIMATE.md, that provides a comprehensive overview of the Wan 2.2 Animate pipeline.

The document covers the high-level workflow, a detailed breakdown of the pipeline's components (masking, model architecture, and relighting), and the end-to-end execution flow.

[deepbeepmeep]

thx. A documentation about Animate would be useful for the end user. But why a guide about the internals of the model ?

[JinJomes]

This would be a great template for all Model Guides here - 1000x more informative and useful in a few minutes than sitting through any half-hour Youtube twonk.

[jsr184]

I wouldn't mind even more in-depth documentation, as I'm currently looking into the black outline issue, and I'm comparing what my ComfyUI pipeline does differently so that the issue doesn't occur. At this moment, I find the Animate pipeline not of much use because of this problem. Well-documented code is priceless.

[deepbeepmeep]

@jsr184 I did reply in the corresponding issue: just disable See Through mask and you will fall back to the default Animate implementation.

I can understand the need to document the internals of WanGP but this should be addressed in a different area (a wiki ?) not in the guides area which are for end users. On the other hand as I pointed earlier I am sure there is some demand for advice on how to use Animate and this guide once it has been simplified could be a good starting point.