Update webpack configuration docs

According to recent updates, we now import flexboxgrid directly, not via SCSS files. This means that flexboxgrid is the one that users should be targeting in their loader configuration, not react-flexbox-grid.

Fixes #21.
Refs #26.

README.md

@@ -19,27 +19,24 @@ Although there are other ways to use React Toolbox, the recommended way is to cr
 
 ### Basic webpack configuration
 
-You probably don't want to load all dependencies with the CSS Modules feature, so you can add this very targeted piece of configuration as a webpack loader:
-
-Note: To prevent [Empty ClassName Issue](https://github.com/roylee0704/react-flexbox-grid/issues/21). It is important to append '?modules' to css-loader.
+You should configure webpack to load flexboxgrid with [CSS Modules](https://github.com/webpack/css-loader#css-modules), otherwise components from react-flexbox-grid will just have [empty class names](https://github.com/roylee0704/react-flexbox-grid/issues/21):
 
 ```js
 {
-  test: /\.scss$/,
-  loaders: ['style', 'css?modules', 'sass'],
-  include: path.resolve(__dirname, './node_modules/react-flexbox-grid'),
+  test: /\.css$/,
+  loader: 'style!css?modules',
+  include: /flexboxgrid/,
 }
 ```
 
-
-But make sure your other CSS loaders don't pick it up. If, for example, there is a loader which includes all SCSS files in `node_modules`, you can exclude this module by using `exclude`:
+If you have other loaders which affect `flexboxgrid`, make sure to exclude it:
 
 ```js
 {
-  test: /\.scss$/,
-  loaders: ['style', 'css?foo=bar', 'sass?config&anotherConfig'],
-  include: path.resolve(__dirname, './node_modules'),
-  exclude: path.resolve(__dirname, './node_modules/react-flexbox-grid'),
+  test: /\.css$/,
+  loader: 'style!css!postcss',
+  include: path.join(__dirname, 'node_modules'), // this also includes flexboxgrid
+  exclude: /flexboxgrid/, // so we are excluding it
 }
 ```