[hotfix] [docs] Link documentation contribution guide from CONTRIBUTING

[lurui1997]

What is the purpose of the change

Point new contributors from .github/CONTRIBUTING.md to the official Documentation Contribution Guide so doc-only work (preview under docs/, JIRA expectations) is discoverable next to the code contribution links.

Brief change log

• Added one sentence and link to https://flink.apache.org/how-to-contribute/contribute-documentation/

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies: no
• The public API: no
• The serializers: no
• The runtime per-record code paths: no
• Deployment or recovery: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no

Made with Cursor

[lurui1997]

Submitted as a [hotfix] [docs] change per .github/PULL_REQUEST_TEMPLATE.md (no JIRA for trivial doc onboarding tweaks). Happy to fold into a FLINK ticket if a committer prefers.

[flinkbot]

CI report:

• 1467ee4 Azure: SUCCESS

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