README: add FAQ explaining why Skill/Subagent/MCP are intentionally out of scope

Author: he-yufeng

README.md

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 I wrote [7 articles](article/) breaking down Claude Code's architecture — the agent loop, tool system, context compression, streaming executor, multi-agent, and 44 hidden feature flags. If you want to understand *why* CoreCoder is designed this way, start there.
 
+## FAQ
+
+**Does CoreCoder support Skills / Subagents / MCP?**
+
+No, and that's intentional. CoreCoder is the minimal runnable core — agent loop, tools, streaming, compaction. Skills, Subagents, MCP, hooks, and plugins are upper-layer features that Claude Code layers on top; if CoreCoder had them too it would stop being a teaching artifact. The architecture articles above cover how those systems work in Claude Code, so you can add them yourself if you need to.
+
+If you want Skills specifically, the recipe is small: scan `~/.claude/skills/*.md` at startup, list their titles in the system prompt, and let the agent ask for a skill by name before you inline that file's body into the conversation.
+
 ## License
 
 MIT. Fork it, learn from it, ship something better. A mention of this project is appreciated.

README_CN.md

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 我还写了 [7 篇 Claude Code 架构深度导读](article/)：Agent 循环、工具系统、上下文压缩、流式执行、多 Agent、隐藏功能。想知道 CoreCoder 为什么这样设计，从那里开始。
 
+## FAQ
+
+**CoreCoder 支持 Skill / Subagent / MCP 吗？**
+
+不支持，这是刻意的。CoreCoder 只保留可运行的最小核心 —— agent 循环、工具、流式、压缩。Skill、Subagent、MCP、hook、plugin 都是 Claude Code 在上层加的特性；如果 CoreCoder 也全都做了，就不再是一个可读的教学产物。上面的架构导读系列讲了 Claude Code 里这些系统是怎么工作的，你可以照着自己加。
+
+如果你只是想要 Skill，配方很简单：启动时扫 `~/.claude/skills/*.md`，把标题列进 system prompt，让 agent 按名字请求某个 skill，再把那个文件的内容 inline 进对话就行了。
+
 ## License
 
 MIT。Fork，然后拿去造更好的东西，如果能标注此出处就更好了。