README.md: Update

Author: xqq

README.md

@@ -33,9 +33,8 @@ npm install --save flv.js
 
 ## Build
 ```bash
-npm ci                 # install dependencies / dev-dependences
-npm run build:debug    # debug version flv.js will be emitted to /dist
-npm run build          # minified release version flv.min.js will be emitted to /dist
+npm ci         # install dependencies / dev-dependences
+npm run dev    # watch file change and build debug version on the fly
 ```
 
 [cnpm](https://github.com/cnpm/cnpm) mirror is recommended if you are in Mainland China.
@@ -78,9 +77,9 @@ See [api.md](docs/api.md)
 
 ## Debug
 ```bash
-npm install          # install dev-dependences
-npm install -g gulp  # install build tool
-npm run dev          # with incremental compile and auto reload
+npm ci                 # install dependencies / dev-dependences
+npm run build:debug    # debug version flv.js will be emitted to /dist
+npm run build          # minimized release version flv.min.js will be emitted to /dist
 ```
 
 ## Design