Update README.md

Author: tingyuan

README.md

@@ -1,5 +1,5 @@
 # vue-flags-webpack-plugin
-Remove useless code by setting flags in .vue SFC file
+Remove useless code by setting flags in .vue SFC file(works with [`vue-loader`](https://github.com/vuejs/vue-loader))
 
 [![npm version](https://img.shields.io/npm/v/vue-flags-webpack-plugin.svg)](https://www.npmjs.com/package/vue-flags-webpack-plugin)
 [![Build Status](https://travis-ci.org/lovetingyuan/vue-flags-webpack-plugin.svg?branch=master)](https://travis-ci.org/lovetingyuan/vue-flags-webpack-plugin)
@@ -100,7 +100,7 @@ vue component:
 ```
 
 ### Caveats
-- **[`postcss-loader`](https://postcss.org/) is required to support flags in css**
+- **[`postcss-loader`](https://github.com/postcss/postcss-loader) is required to support flags in css**
   - for version>=15, see: https://vue-loader.vuejs.org/guide/pre-processors.html#postcss
   - for older `vue-loader`, see: https://vue-loader-v14.vuejs.org/zh-cn/features/postcss.html (*`vue-loader` which version < 15 is deprecated, do not use it.*)