docs(readme): update READMEs and add English doc placeholders

[darion-yaphet]

• Fix outdated Travis CI badge in README_cn.md to GitHub Actions
• Unify all doc links in README.md to point to docs/en/ directory
• Add references for bthread tracer, coroutine, circuit breaker, RDMA, Bazel support
• Create 39 English placeholder docs pointing to Chinese versions
• Create Chinese placeholder for couchbase_example

What problem does this PR solve?

Issue Number: resolve

Problem Summary:

The README.md and README_cn.md have not been updated for a long time. README_cn.md still uses the outdated Travis CI badge, README.md links many docs to docs/cn/ instead of docs/en/, and several newer docs (bthread tracer, coroutine, circuit breaker, RDMA, Bazel support, etc.) are not referenced in either README. Additionally, 39 docs exist only in Chinese with no English counterpart.

What is changed and the side effects?

Changed:

• Fixed CI badge in README_cn.md from Travis CI to GitHub Actions (Linux + macOS)
• Unified all doc links in README.md to point to docs/en/ instead of docs/cn/
• Added new doc references in both READMEs: bthread tracer, bthread tagged task group, coroutine, circuit breaker, RDMA, Bazel support, Wireshark baidu_std dissector plugin
• Created 39 English placeholder docs under docs/en/ that point readers to the corresponding Chinese version and invite translation contributions
• Created 1 Chinese placeholder doc (docs/cn/couchbase_example.md) pointing to the English version

Side effects:

• Performance effects: None
• Breaking backward compatibility: None. All existing doc links remain valid; only new files and link path updates are introduced.

What is changed and the side effects?

Changed:

Side effects:

• Performance effects:

• Breaking backward compatibility:

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.