Added gitpod config (#3349)

.gitpod.yml

+ports:
+- port: 8000
+  onOpen: open-preview
+tasks:
+- init: npm install
+  command: npm start

README.md

@@ -112,6 +112,12 @@ $ npm run docker-prod:dev
 $ npm run docker-prod:build
 ```
 
+### Use Gitpod
+
+Open the project in Gitpod (free online dev environment for GitHub) and start coding immediately.
+
+[![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/ant-design/ant-design-pro)
+
 More instructions at [documentation](http://pro.ant.design/docs/getting-started).
 
 ## Browsers support