chore: add extraction info to readme (#663)

* chore: add extraction info to readme

* Update README.md

README.md

@@ -28,6 +28,35 @@ const StyledButton = styled.button`
 </ClassNames>
 ```
 
+### Extract styles
+
+Turn on extraction and all components styled in your app and sourced through NPM will have their runtime stripped and styles extracted to an atomic style sheet.
+
+```diff
+-import { CC, CS } from '@compiled/react/runtime';
+-
+-const _2 = '._syaz1q9v{color: hotpink}';
+-const _ = '._1wybfyhu{font-size: 48px}';
+-
+export const LargeHotPinkText = () => (
+-  <CC>
+-   <CS>{[_, _2]}</CS>
+    <span className="_syaz1q9v _1wybfyhu">Hello world</span>
+-  </CC>
+);
+```
+
+```css
+._1wybfyhu {
+  font-size: 48px;
+}
+._syaz1q9v {
+  color: hotpink;
+}
+```
+
+See [CSS extraction](https://compiledcssinjs.com/docs/css-extraction-webpack) for more information.
+
 ## Installation
 
 Install the [React](https://reactjs.org/) package.