docs: update main function return values, add html-webpack-plugin example (#98)

* Updated Readme.md 

Updated Readme.md to reflect actual middleware behavior, also fixed actual name of the property containing devMiddleware
Added example usage with html-webpack-plugin

* chore: slight verbiage modification

Author: josser

README.md

@@ -60,13 +60,14 @@ koaWebpack({ .. options .. })
 
 ### koaWebpack([options])
 
-Returns an `Object` containing:
+Returns a `Promise` which resolves the server `middleware` containing the
+following additional properties:
 
 - `close(callback)` *(Function)* - Closes both the instance of `webpack-dev-middleware`
 and `webpack-hot-client`. Accepts a single `Function` callback parameter that is
 executed when complete.
-- `client` *(Object)* - An instance of `webpack-hot-client`.
-- `dev` *(Object)* - An instance of `webpack-dev-middleware`
+- `hotClient` *(Object)* - An instance of `webpack-hot-client`.
+- `devMiddleware` *(Object)* - An instance of `webpack-dev-middleware`
 
 ## Options
 
@@ -164,6 +165,24 @@ For more details please refer to:
 [webpack-dev-middleware](https://github.com/webpack/webpack-dev-middleware#server-side-rendering)
 
 
+## Using with html-webpack-plugin
+
+When using with html-webpack-plugin, you can access dev-middleware in-memory filesystem to serve index.html file:
+
+```js
+koaWebpack({
+  config: webpackConfig
+}).then(middleware => {
+  app.use(middleware)
+
+  app.use(async ctx => {
+    const filename = path.resolve(webpackConfig.output.path, 'index.html')
+    ctx.response.type = 'html'
+    ctx.response.body = middleware.devMiddleware.fileSystem.createReadStream(filename)
+  })
+})
+```
+
 ## Contributing
 
 Please take a moment to read our contributing guidelines if you haven't yet done so.