chore: document hotswap plugin watched-packages setting

References vaadin/flow#20389

articles/flow/configuration/live-reload/hotswap-agent.adoc

@@ -81,6 +81,8 @@ You should disable other reloading or hot swapping solutions. For example, disab
 
 The live reload "quiet time" -- which is in milliseconds since the last Java change before refreshing the browser -- can be adjusted with the parameter `vaadin.liveReloadQuietTime` in the [filename]`hotswap-agent.properties` file. The default is 1000 ms. Increase this value if you notice the browser refreshing before modified Java files have been fully compiled. 
 
+It is recommended to configure the Vaadin Hotswap plugin to watch only for application classes by setting the `vaadin.watched-packages` property in the [filename]`hotswap-agent.properties` file. The value should be a comma-separated list of Java package names, for example: `com.example.ui,com.example.endpoints`.
+
 Changes to some parts of the Java code, such application startup listeners, won't have any effect until the server is restarted and the startup listeners run again. For these you need to restart the server.
 
 If you're using the <<{articles}/flow/advanced/preserving-state-on-refresh#,`@PreserveOnRefresh`>> annotation, the same view instance is reused when the browser is reloaded. That means changes aren't necessarily visible until the view is opened in another browser tab.