Update documentation with how to change config in the top level readm…

README.md

@@ -22,6 +22,7 @@ in which case you may not even need the asset pipeline. This is mostly relevant
 - [Installation](#installation)
   - [Usage](#usage)
   - [Development](#development)
+  - [Webpack configuration](#webpack-configuration)
 - [Integrations](#integrations)
   - [React](#react)
   - [Angular with TypeScript](#angular-with-typescript)
@@ -173,6 +174,10 @@ when running `./bin/webpack-dev-server` binstub:
 
 **Note:** Don't forget to prefix `ruby` when running these binstubs on windows
 
+### Webpack configuration
+
+See [docs/Webpack](docs/webpack.md) for modifying webpack configuration and loaders.
+
 ## Integrations
 
 Webpacker ships with basic out-of-the-box integration for React, Angular, Vue and Elm.

docs/webpack.md

@@ -8,7 +8,7 @@ production environments in `config/webpack/*.js`. You can configure each individ
 environment in their respective files or configure them all in the base
 `config/webpack/environment.js` file.
 
-By default, you shouldn't have to make any changes to `config/webpack/*.js`
+By default, you don't need to make any changes to `config/webpack/*.js`
 files since it's all standard production-ready configuration. However,
 if you do need to customize or add a new loader, this is where you would go.
 
@@ -36,6 +36,14 @@ const customConfig = require('./custom')
 module.exports = merge(environment.toWebpackConfig(), customConfig)
 ```
 
+If you need access to configs within Webpacker's configuration, you can import them like this:
+```js
+const config = require('@rails/webpacker/package/config');
+const asset_host = require('@rails/webpacker/package/asset_host');
+
+console.log(asset_host.publicPathWithHost);
+```
+
 **Note:** You will have to merge custom config to all env where you want that config
 to be available. In above case, it will be applied to development environment.