website: add example.

core/README.md

@@ -142,6 +142,35 @@ export default function App() {
 }
 ```
 
+## Show LineNumbers
+
+```jsx
+import rehypePrism from 'rehype-prism-plus';
+import React, { useState } from "react";
+import CodeEditor from '@uiw/react-textarea-code-editor';
+
+export default function App() {
+  const [code, setCode] = useState(
+    `function add(a, b) {\n  return a + b;\n}`
+  );
+  return (
+    <CodeEditor
+      value={code}
+      language="js"
+      placeholder="Please enter JS code."
+      onChange={(evn) => setCode(evn.target.value)}
+      rehypePlugins={[
+        [rehypePrism, { ignoreMissing: true, showLineNumbers: true }]
+      ]}
+      style={{
+        backgroundColor: "#f5f5f5",
+        fontFamily: 'ui-monospace,SFMono-Regular,SF Mono,Consolas,Liberation Mono,Menlo,monospace',
+      }}
+    />
+  );
+}
+```
+
 ## Support Nextjs
 
 Use examples in nextjs. [#31](https://github.com/uiwjs/react-textarea-code-editor/issues/31#issuecomment-909363339)