docs: fix Chinese mining guide relative links

[yyswhsccc]

What Changed

• Fixed three broken relative links in docs/zh-CN/MINING_GUIDE.md.
• Updated the two top-level document links to resolve from docs/zh-CN/.
• Updated the troubleshooting FAQ link to resolve to the shared docs FAQ.

Why It Matters

The Chinese mining guide currently sends readers to missing Markdown targets for install prerequisites, CPU antiquity details, and troubleshooting. This keeps the translated guide navigable without changing the surrounding content.

Validation

• python3 focused Markdown relative-link scan for docs/zh-CN/MINING_GUIDE.md -> checked 6 relative links, missing_count=0.
• git diff --check upstream/main...HEAD -- docs/zh-CN/MINING_GUIDE.md -> passed.
• GitHub CI / test is still red with the same repo-wide baseline failure seen on unrelated docs-only PRs; that baseline is being handled separately in test: restore repo-wide CI baseline expectations #6711, without broadening this docs PR.

Scope / Risk

• Touched files/subsystems: docs/zh-CN/MINING_GUIDE.md
• Documentation-only change; no runtime behavior, API, protocol, or dependency changes.
• Related bounty issue: [BOUNTY] Report a Bug — 5-15 RTC #305

wallet: RTC47bc28896a1a4bf240d1fd780f4559b242bcd945

[yyswhsccc]

@Scottcjn This PR is ready for maintainer review.

Validation evidence is listed in the PR body. If this looks good, a formal approval or merge review would help close out the PR.

[jaxint]

Thanks for contributing! 🦀

Code review completed. Nice work! 🚀

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Wallet: AhqbFaPBPLMMiaLDzA9WhQcyvv4hMxiteLhPk3NhG1iG

[yyswhsccc]

@jaxint Thanks for reviewing this. GitHub currently shows this as a comment-only review rather than a formal approval.

Could you re-review when you have a chance? If this looks good, a formal approval would help close out the review.

[jaxint]

Great contribution! 🔍 Reviewed and looks solid.

[jaxint]

LGTM! Thanks for contributing to RustChain. Approved.

[jaxint]

Well done! This contribution adds real value to the project.