Update doc about EROFS support

[BigVan]

What is the version of your Accelerated Container Image

No response

What would you like to be added?

Since erofs conversion has been supported for a while. Please update the document if you have time～
https://github.com/containerd/accelerated-container-image/blob/main/docs/MULTI_FS_SUPPORT.md
@hsiangkao

Why is this needed for Accelerated Container Image?

update doc

Are you willing to submit PRs to contribute to this feature?

• Yes, I am willing to implement it.

[hsiangkao]

Ok, let me find time to document it, but really it doesn't have the traditional mkfs option meaning.

[BigVan]

Or wait until we finish optimizing the conversion process before updating
:D

[hsiangkao]

Or wait until we finish optimizing the conversion process before updating :D

Sounds good to me. I think finishing API integration is the first priority for us to get the best mkfs performance.