chore: update NpmPackage assets reference

Update the npm assets referencing to match
new functionality.

part of vaadin/flow#22515

Author: caalador

articles/styling/advanced/npm-packages.adoc

@@ -54,7 +54,7 @@ public class MyComponent implements Component {
 [#fonts-and-images-from-npm]
 == Using Static Resources from npm Packages
 
-The `assets` field in the [annotationname]`@NpmPackage` annotation allows you to copy assets from npm packages into the static resource folder (i.e., the `VAADIN/static` folder), allowing you to references them from Java source code and from the browser.
+The `assets` field in the [annotationname]`@NpmPackage` annotation allows you to copy assets from npm packages into the static resource folder, allowing you to references them from Java source code and from the browser staring the request as `assets/{npm_asset_path}`.
 
 The `assets` field syntax looks like this in general: `"asset/glob/pattern:local/target/path"`. The first part defines which files from the npm package should be copied, and it can be a “glob” pattern. 
 The second part, after the colon, defines where matching resources are copied under the resources folder. You can define multiple asset mappings for a single package annotation.
@@ -73,13 +73,13 @@ The second part, after the colon, defines where matching resources are copied un
 public class MyComponent implements Component {
     public MyComponent() {
 // tag::usage[]
-        add(new Image("VAADIN/static/fontawesome/icons/snowflake.svg",
+        add(new Image("assets/fontawesome/icons/snowflake.svg",
             "snowflake"));
 // end::usage[]
     }
 }
 ----
 
-In the previous example, the `fortawesome` file `svgs/regular/snowflake.svg` is copied to `VAADIN/static/fontawesome/icons/snowflake.svg` and can be accessed with that path in the application code and CSS stylesheets.
+In the previous example, the `fortawesome` file `svgs/regular/snowflake.svg` is copied to `VAADIN/static/assets/fontawesome/icons/snowflake.svg` and can be accessed with the path `assets/fontawesome/icons/snowflake.svg`  in the application code and CSS stylesheets.
 
 [discussion-id]`3e46fe3b-00d6-4cf7-908c-342a364210db`