doc: add example in document. (#151)

Author: jaywcjlove

README.md

@@ -56,6 +56,56 @@ function App() {
 }
 ```
 
+## Highlight line or character
+
+[![Open in CodeSandbox](https://codesandbox.io/embed/https-github-com-uiwjs-react-textarea-code-editor-issues-151-nsm7qp?fontsize=14&hidenavigation=1&theme=dark)
+
+```jsx
+import CodeEditor from '@uiw/react-textarea-code-editor';
+import rehypePrism from "rehype-prism-plus";
+import rehypeRewrite from "rehype-rewrite";
+import "./styles.css";
+
+function App() {
+  const [code, setCode] = React.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)}
+      padding={15}
+      rehypePlugins={[
+        [rehypePrism, { ignoreMissing: true }],
+        [
+          rehypeRewrite,
+          {
+            rewrite: (node, index, parent) => {
+              if (node.properties?.className?.includes("code-line")) {
+                if (index === 0 && node.properties?.className) {
+                  node.properties.className.push("demo01");
+                  // console.log("~~~", index, node.properties?.className);
+                }
+              }
+              if (node.type === "text" && node.value === "return" && parent.children.length === 1) {
+                parent.properties.className.push("demo123");
+              }
+            }
+          }
+        ]
+      ]}
+      style={{
+        fontSize: 12,
+        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)