docs: add KernelSU migration guidance

[uniStark]

Add a Chinese migration guide for users moving APModule installations from KernelSU to APatch. It documents the supported workflow, avoids copying internal state directories, calls out path/Zygisk/SELinux compatibility checks, and gives rollback guidance.

This follows the question in Discussion #354 and links back to the existing APM documentation.

[uniStark]

关闭重复提交，保留由 tony403 提交的同一份迁移文档 PR #1572，避免给维护者造成重复审阅。