Add a demo for multiple loaders (#5076)

docs/guide/webpack.md

@@ -81,6 +81,10 @@ module.exports = {
       .use('graphql-tag/loader')
         .loader('graphql-tag/loader')
         .end()
+      // Add another loader
+      .use('other-loader')
+        .loader('other-loader')
+        .end()
   }
 }
 ```