Added Gitpod support (ant-design#14307)

Author: svenefftinge

Diff for: .gitpod.yml

@@ -0,0 +1,8 @@
+ports:
+- port: 8001
+  onOpen: open-preview
+tasks:
+- before: >
+    export DEV_HOST=$(gp url 8001)
+  init: npm install
+  command: npm start

Diff for: README.md

@@ -100,6 +100,12 @@ See [i18n](http://ant.design/docs/react/i18n).
 
 ## ⌨️ Development
 
+Use Gitpod, a free online dev environment for GitHub.
+
+[![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/ant-design/ant-design)
+
+Or clone locally:
+
 ```bash
 $ git clone [email protected]:ant-design/ant-design.git
 $ cd ant-design

Diff for: site/bisheng.config.js

@@ -123,6 +123,11 @@ module.exports = {
     return config;
   },
 
+  devServerConfig: {
+    public: process.env.DEV_HOST || 'localhost',
+    disableHostCheck: !!process.env.DEV_HOST,
+  },
+
   htmlTemplateExtraData: {
     isDev,
     usePreact,