docs: add guide for global scss loading (#861)

* update docs for global scss loading

per this comment thread: vuejs/vue-loader#328 (comment)

* be more generic about webpack rule

* update text

Author: westwick

docs/en/configurations/pre-processors.md

@@ -37,6 +37,40 @@ Contrary to what its name indicates, [*sass*-loader](https://github.com/jtangeld
 
 See the [Advanced Loader Configuration](./advanced.md) Section for further information about how to configure vue-loader.
 
+#### Loading a global settings file
+
+A common request is to be able to load a settings file in each component without the need to explicity import it each time, e.g. to use scss variables globally throughout all components. To accomplish this:
+
+``` bash
+npm install sass-resources-loader --save-dev
+```
+
+Then add the following webpack rule:
+
+``` js
+{
+  loader: 'sass-resources-loader',
+  options: {
+    resources: path.resolve(__dirname, '../src/style/_variables.scss')
+  }
+}
+```
+
+As an example, if you are using [vuejs-templates/webpack](https://github.com/vuejs-templates/webpack), modify `build/util.js` like so:
+
+``` js
+scss: generateLoaders('sass').concat(
+  {
+    loader: 'sass-resources-loader',
+    options: {
+      resources: path.resolve(__dirname, '../src/style/_variables.scss')
+    }
+  }
+),
+```
+
+It is recommended to only include variables, mixins, etc. in this file, to prevent duplicated css in your final, compiled files. 
+
 ### JavaScript
 
 All JavaScript inside Vue components are processed by `babel-loader` by default. But you can of course change it: