docs: add README for every subdirectory

33 agent READMEs, 14 hand READMEs, 2 plugin READMEs
(echo-memory + hooks), and 2 skill READMEs
(custom-skill-prompt + custom-skill-python).

Each README documents the component's purpose, configuration,
and usage based on its TOML definition.

hands/linkedin/README.md

@@ -0,0 +1,32 @@
+# LinkedIn Hand
+
+Autonomous LinkedIn manager -- profile optimization, content creation, networking, and professional engagement.
+
+## Configuration
+
+| Field | Value |
+|-------|-------|
+| Category | `communication` |
+| Agent | `linkedin-hand` |
+| Routing | `linkedin`, `profile optimization`, `professional networking` |
+
+## Integrations
+
+- **LINKEDIN_ACCESS_TOKEN** -- OAuth 2.0 access token from the LinkedIn Developer Portal.
+
+## Settings
+
+- **Content Style** -- `thought_leader`, `educational`, `storyteller`, `data_driven`, `conversational`
+- **Post Frequency** -- `1_weekly`, `3_weekly`, `5_weekly`, `1_daily`
+- **Content Topics** -- Comma-separated topics to create content about
+- **Auto Engage** -- Automatically like/comment on relevant posts (default: off)
+- **Approval Mode** -- Queue posts for review before posting (default: on)
+- **Hashtag Count** -- `0`, `3`, `5`
+- **Target Audience** -- `peers`, `recruiters`, `clients`, `general`
+- **Language** -- `en`, `zh`, `es`, `auto`
+
+## Usage
+
+```bash
+librefang hand run linkedin
+```