docs(configuration) Added documentation for [contenthash] #6839 (#2085)

* Added documentation for [contenthash] #6839

* Fix TravisCI build

* remove extra space before colon

* Fix lint issues

* Remove semicolon

Author: FadySamirSadek

src/content/configuration/output.md

@@ -10,6 +10,7 @@ contributors:
   - fvgs
   - dhurlburtusa
   - MagicDuck
+  - fadysamirsadek
   - byzyk
   - madhavarshney
 ---
@@ -264,6 +265,17 @@ module.exports = {
 };
 ```
 
+Using hashes generated for extracted content:
+
+```js
+module.exports = {
+  //...
+  output: {
+    filename: '[contenthash].bundle.css'
+  }
+};
+```
+
 Make sure to read the [Caching guide](/guides/caching) for details. There are more steps involved than just setting this option.
 
 Note this option is called filename but you are still allowed to use something like `"js/[name]/bundle.js"` to create a folder structure.