Add extractStyle API description to README

close #187

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Author: afc163

README.md

@@ -75,6 +75,31 @@ Create theme object. When same algorithm provided, it will return same object.
 
 Since `@ant-design/cssinjs` use strong constraints for cache hit performance, we recommend to view demo `basic.tsx` for usage and `animation.tsx` for animation usage.
 
+### extractStyle
+
+Extracts the styles from the cache and returns them as a string.
+
+#### Parameters
+
+- `cache` (Cache): The cache instance containing the styles.
+- `options` (object | boolean, optional): Options for extracting the styles.
+  - `plain` (boolean, optional): If true, the styles will be returned in plain format. Default is false.
+  - `types` (string | string[], optional): The types of styles to extract. Default is ['style', 'token', 'cssVar'].
+
+#### Returns
+
+- (string): The extracted styles as a string.
+
+#### Example
+
+```typescript
+import extractStyle from '@ant-design/cssinjs';
+
+const cache = /* your cache instance */;
+const styles = extractStyle(cache, { plain: true, types: ['style', 'token'] });
+console.log(styles);
+```
+
 ## Transform
 
 When you need transform CSSObject before inject style. You can use `transformers` to handle this: