doc: add block dev doc

README.md

-# umi-blocks
+# pro-blocks
 
-Official collection of some high quality blocks.
+umi blocks of Ant Design Pro.
 
 ## Usage
 
 ```shell
-$ umi block list
-$ umi block add [A block name in list, or any github address of a umi block]
+$ umi block add [the github url of block]
 ```
 
 You can visit umi [doc](https://umijs.org/guide/block.html) for find out more info about umi block.
 
 ## Contribute
 
-You can create a umi block and make a PR for us!
+```shell
+$ cd [some block]
+$ yarn # or npm install
+$ yarn run dev # or npm run dev
+```
 
-How to create a block:
+Or
 
 ```shell
-$ yarn create umi --block
+$ yarn # or npm install
+$ APP_ROOT=[some block] yarn run dev # or APP_ROOT=[someblock] npm run dev
 ```

package.json

 {
   "private": true,
   "scripts": {
+    "dev": "umi dev",
     "lint:style": "stylelint \"src/**/*.less\" --syntax less",
     "lint": "eslint --ext .js src mock tests && npm run lint:style",
     "lint:fix": "eslint --fix --ext .js src mock tests && npm run lint:style",