Add documentation for contributing a blog post

[wuchong]

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Description

Summary

The project currently lacks clear guidelines for community members who want to contribute blog posts. This issue tracks the creation of a comprehensive guide that outlines the submission process, content requirements, and publication workflow.

Motivation

A well-defined contribution process for blog posts will encourage community engagement, ensure consistent content quality, and streamline the editorial review pipeline. Clear documentation will help contributors understand expectations regarding topic selection, formatting standards, technical accuracy, and appropriate tone.

There is a basic workflow about how to contribute blog post in https://github.com/apache/fluss-blog/blob/main/README.md

Willingness to contribute

• I'm willing to submit a PR!