chore: add gitpod config.

Author: jaywcjlove

.gitpod.yml

@@ -0,0 +1,6 @@
+ports:
+  - port: 3000
+    onOpen: open-preview
+tasks:
+  - init: npm install
+    command: npm run build && npm run start

README.md

@@ -5,6 +5,7 @@
 [![Open in unpkg](https://img.shields.io/badge/Open%20in-unpkg-blue)](https://uiwjs.github.io/npm-unpkg/#/pkg/@uiw/react-codemirror/file/README.md)
 [![npm version](https://img.shields.io/npm/v/@uiw/react-codemirror.svg)](https://www.npmjs.com/package/@uiw/react-codemirror)
 [![Coverage Status](https://uiwjs.github.io/react-codemirror/coverage/badges.svg)](https://uiwjs.github.io/react-codemirror/coverage/lcov-report/)
+[![Open in Gitpod](https://shields.io/badge/Open%20in-Gitpod-green?logo=Gitpod)](https://gitpod.io/#https://github.com/uiwjs/react-codemirror)
 
 CodeMirror component for React. Demo Preview: [@uiwjs.github.io/react-codemirror](https://uiwjs.github.io/react-codemirror/)