Update Tailwind compiler explanation in utility classes (#5433)

Clarified the Tailwind compiler process and its limitations regarding class names in the browser inspector.

Author: jouni

articles/styling/utility-classes.adoc

@@ -69,7 +69,9 @@ warningBox.addClassNames("bg-orange-400 p-20");
 
 A complete list of Tailwind utility classes is available in the link:https://tailwindcss.com/[Tailwind CSS documentation,window=_blank].
 
-When enabled, the Vaadin build process feeds all source files through the Tailwind compiler that collects all Tailwind class names used in them and compiles a static stylesheet that contains CSS only for the identified class names.
+.Class names need to be present in the source code.
+[IMPORTANT]
+When enabled, the Vaadin build process feeds all source files through the Tailwind compiler. The compiler then collects all Tailwind class names used in the source files and compiles a static stylesheet that contains CSS only for the identified class names. That means you can't use any other class names in the browser inspector, for example, when degugging or testing in the browser.
 
 == Lumo Utility Classes