docs: 添加 Agent Skill 到项目仓库

- 复制 reader-digest-flow skill 到 skills/ 目录（含 SKILL.md + references/）
- README 新增 Agent Skill 章节说明供 Agent 使用的工作流

skills/reader-digest-flow/references/feishu-format-notes.md

@@ -0,0 +1,26 @@
+# Feishu Markdown Format Notes
+
+## Background
+
+Hermes' Feishu gateway (`gateway/platforms/feishu.py`) sends outbound messages
+through `_build_outbound_payload`, which checks content for markdown patterns
+to decide how to send:
+
+- Content matches `_MARKDOWN_HINT_RE` (bold, lists, code, links, etc.)
+  → sent as Feishu `post` type using `md` elements → renders correctly.
+
+- Content matches `_MARKDOWN_TABLE_RE` (a markdown table header + separator)
+  → **entire message** forced to `text` type (plain text) → no rendering.
+
+The root cause is that the `_build_markdown_post_payload` helper wraps content
+in `{"tag": "md", "text": "..."}` elements, and Feishu's `md` element does not
+support table rendering. There is no table-to-native-Feishu-table conversion.
+
+## Rules for Feishu output
+
+- **Never use markdown tables** in any message delivered via Feishu.
+  A single table anywhere in the message forces the whole message to plain text.
+- Prefer bullet lists, sections with headings, or inline formatting instead.
+- Bold (`**bold**`), inline code (`` `code` ``), unordered lists (`- item`),
+  ordered lists (`1. item`), and links all work correctly.
+- Code fences (``` ``` ```) work but may have edge cases with trailing content.