Add a description of the zfile data section in the spec, and explain the difference in its CRC32.

[liulanzheng]

What is the version of your Overlaybd

No response

What would you like to be added?

Add a description of the zfile data section in the spec, and explain the difference in its CRC32.

Why is this needed for Overlaybd?

To avoid any issues for zfile developers

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

• [ ] Yes, I am willing to implement it.