docs: add Why section to README per publishing SOP

Add 'Why Smart Illustrator?' section explaining use cases and target audience, following SOP best practices for standalone repo README.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: axtonliu

README.md

@@ -14,6 +14,14 @@ Intelligent article illustration Skill for Claude Code with **dual-engine system
 > - My primary focus is demonstrating how tools and systems work together, not maintaining this codebase.
 > - If you encounter issues, please submit a reproducible case (input + output file + steps to reproduce).
 
+## Why Smart Illustrator?
+
+Creating illustrations for articles is time-consuming: manual design takes hours, stock photos lack context, and generic AI tools don't understand article structure. Smart Illustrator combines intelligent position detection, dual-engine system (Mermaid + Gemini), and cover learning to generate contextual illustrations in minutes.
+
+**Who it's for:** Newsletter writers, YouTube creators, technical bloggers, course instructors.
+
+**When to use:** When you need high-quality illustrations for articles, YouTube thumbnails with best practices, or consistent visual style across content series.
+
 ## Features
 
 - **Dual Engine System**: Auto-selects Mermaid or Gemini based on content type

README.zh-CN.md

@@ -16,6 +16,14 @@ Claude Code 的智能文章配图 Skill，采用**双引擎系统**：根据内
 > - 我的主要目标是展示工具和系统如何协同工作，而非维护这个代码库。
 > - 如遇问题，请提交可复现的案例（输入 + 输出文件 + 复现步骤）。
 
+## 为什么选择 Smart Illustrator？
+
+为文章配图很费时间：手动设计需要数小时，图库图片缺乏定制性，通用 AI 工具不理解文章结构。Smart Illustrator 结合智能位置检测、双引擎系统（Mermaid + Gemini）和封面学习，几分钟内生成符合上下文的插图。
+
+**适合谁用：** Newsletter 作者、YouTube 创作者、技术博客作者、课程讲师。
+
+**什么时候用：** 需要为文章生成高质量插图、基于最佳实践生成 YouTube 封面图、或保持内容系列视觉风格一致时。
+
 ## 功能特性
 
 - **双引擎系统**：根据内容类型自动选择 Mermaid 或 Gemini