chore: document hotswap plugin watched-packages setting (#3916)

* chore: document hotswap plugin watched-packages setting

References vaadin/flow#20389

* Update hotswap-agent.adoc

* apply review suggestions

* Minor edist to added and surrounding text.

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Co-authored-by: Mikhail Shabarov <[email protected]>
Co-authored-by: Jouni Koivuviita <[email protected]>
Co-authored-by: Russell J.T. Dyer <[email protected]>

Author: 4 people

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

@@ -77,11 +77,13 @@ IntelliJ doesn't by default compile a Java file when you save it. If your habit
 
 == Additional Considerations
 
-You should disable other reloading or hot swapping solutions. For example, disable the automatic restart in the Jetty Maven plugin if you're using that. Omit or set `<scanIntervalSeconds>` to a value of `0` or less.
+You should disable other reloading or hot swapping solutions. For example, disable the automatic restart in the Jetty Maven plugin if you're using it. Omit or set `<scanIntervalSeconds>` to a value of `0` or less.
 
-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. 
+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 compiled fully.
 
-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.
+You should 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. This improves performance, and prevents unnecessary reloads by limiting the plugin's monitoring to relevant packages. The value given should be a comma-separated list of Java package names (e.g., `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.