docs: enhance README with advanced features including retry configuration, response data handling, and ETag support

Author: Yukaii

nodejs/README.md

@@ -32,6 +32,52 @@ client.getMe().then(me => {
 })
 ```
 
+## Advanced Features
+
+### Retry Configuration
+
+The client supports automatic retry for failed requests with exponential backoff. You can configure retry behavior when creating the client:
+
+```javascript
+const client = new HackMDAPI('YOUR_ACCESS_TOKEN', 'https://api.hackmd.io/v1', {
+  retryConfig: {
+    maxRetries: 3,    // Maximum number of retry attempts
+    baseDelay: 100    // Base delay in milliseconds for exponential backoff
+  }
+})
+```
+
+The client will automatically retry requests that fail with:
+- 5xx server errors
+- 429 Too Many Requests errors
+- Network errors
+
+### Response Data Handling
+
+By default, the client automatically unwraps the response data from the Axios response object. You can control this behavior using the `unwrapData` option:
+
+```javascript
+// Get raw Axios response (includes headers, status, etc.)
+const response = await client.getMe({ unwrapData: false })
+
+// Get only the data (default behavior)
+const data = await client.getMe({ unwrapData: true })
+```
+
+### ETag Support
+
+The client supports ETag-based caching for note retrieval. You can pass an ETag to check if the content has changed:
+
+```javascript
+// First request
+const note = await client.getNote('note-id')
+const etag = note.etag
+
+// Subsequent request with ETag
+const updatedNote = await client.getNote('note-id', { etag })
+// If the note hasn't changed, the response will have status 304
+```
+
 ## API
 
 See the [code](./src/index.ts) and [typings](./src/type.ts). The API client is written in TypeScript, so you can get auto-completion and type checking in any TypeScript Language Server powered editor or IDE.