Fix: Simplify webpack config auto load (#323)

1. Search for webpack config only in the root folder.
2. Only search for webpack.config.js and webpackfile.js.
3. Simplify webpack style guide example.

docs/Configuration.md

@@ -373,7 +373,7 @@ See [Configuring webpack](./Webpack.md) for examples.
 
 Type: `String`
 
-By default Styleguidist will try to find webpack config (`webpack.config.dev.js` or `webpack.config.js`) anywhere in your project and use it. Use this option to specify a custom path to your webpack config.
+By default Styleguidist will try to find `webpack.config.js` in your project’s root directory and use it. Use this option to specify a custom path to your webpack config.
 
 ```javascript
 module.exports = {

docs/Webpack.md

@@ -8,7 +8,7 @@ Styleguidist uses [webpack](https://webpack.js.org/) under the hood and it needs
 
 ## Reusing your project’s webpack config
 
-By default Styleguidist will recursively try to find an existing webpack config (`webpack.config.dev.js` or `webpack.config.js`) in your project and use it.
+By default Styleguidist will try to find `webpack.config.js` in your project’s root directory and use it.
 
 If your webpack config is located somewhere else, add its location to your `styleguide.config.js`: