docs: add README

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: JohnMcLear

README.md

@@ -0,0 +1,87 @@
+# ep_ai_chat
+
+AI chat participant for Etherpad. When users @mention the AI in pad chat, it
+reads the document, understands who wrote what, and responds. It can also edit
+the pad directly when asked.
+
+## Installation
+
+Requires `ep_ai_core`.
+
+```bash
+pnpm run plugins i ep_ai_core ep_ai_chat
+```
+
+Configure the LLM provider in `settings.json` under the `ep_ai_core` key.
+See the [ep_ai_core README](https://github.com/ether/ep_ai_core#readme) for
+full configuration details.
+
+## Usage
+
+Type `@ai` followed by your message in the pad's chat box:
+
+```
+@ai summarize this document
+@ai who wrote the introduction?
+@ai fix the spelling errors in paragraph 3
+```
+
+The AI will respond in chat. If you ask it to make changes and the pad has
+`full` access mode, it will edit the document directly.
+
+## Configuration
+
+Chat-specific settings go under `ep_ai_core.chat` in `settings.json`:
+
+```json
+{
+  "ep_ai_core": {
+    "apiBaseUrl": "https://api.anthropic.com/v1",
+    "apiKey": "sk-ant-...",
+    "model": "claude-sonnet-4-20250514",
+    "chat": {
+      "trigger": "@ai",
+      "authorName": "AI Assistant",
+      "authorColor": "#7c4dff",
+      "systemPrompt": "You are a helpful writing assistant.",
+      "maxContextChars": 50000,
+      "chatHistoryLength": 20,
+      "conversationBufferSize": 10
+    }
+  }
+}
+```
+
+| Setting | Default | Description |
+|---------|---------|-------------|
+| `trigger` | `@ai` | Text that activates the AI in chat |
+| `authorName` | `AI Assistant` | Display name in chat and authorship |
+| `authorColor` | `#7c4dff` | Color for the AI's edits and chat messages |
+| `systemPrompt` | _(built-in)_ | Custom system prompt for the LLM |
+| `maxContextChars` | `50000` | Max characters of pad content sent to the LLM |
+| `chatHistoryLength` | `20` | Number of recent chat messages included as context |
+| `conversationBufferSize` | `10` | Number of conversation turns remembered per pad |
+
+## How Editing Works
+
+When a user asks the AI to change the document, the AI responds with a
+structured edit (find text, replace with new text). The plugin:
+
+1. Locates the exact text in the pad
+2. Applies the change as a native Etherpad changeset
+3. Attributes the edit to the AI author (with the configured color)
+4. Broadcasts the update to all connected clients
+5. Announces the AI in the user list so its color appears in the author palette
+
+If the pad's access mode is `readOnly`, the AI will answer questions but
+decline edit requests. If access is `none`, the AI will not respond at all.
+
+## Conversation Memory
+
+The AI maintains a short conversation buffer per pad. Follow-up messages
+can reference earlier exchanges without repeating context. The buffer is
+kept in memory and resets when the server restarts.
+
+## License
+
+Apache-2.0