docs(config) document devServer sockPort option (#2995)

Author: EugeneHlushko

src/content/configuration/dev-server.md

@@ -1229,6 +1229,23 @@ module.exports = {
 };
 ```
 
+## `devServer.sockPort`
+
+`number` `string`
+
+Tells `devServer` to use provided socket port.
+
+__webpack.config.js__
+
+```javascript
+module.exports = {
+  //...
+  devServer: {
+    sockPort: 8080
+  }
+};
+```
+
 
 ## `devServer.staticOptions`