docs: Update Getting started documentation (#17975)

This PR adds some sentences to explain the process of "Syncing via UI" screenshots to have a good understanding of the process on the UI.

Signed-off-by: Rodolfo Martínez Vega <rodomar@outlook.com>

docs/getting_started.md

@@ -214,6 +214,12 @@ events, and assessed health status.
 
 ### Syncing via UI
 
+On the Applications page, click on *Sync* button of the guestbook application:
+
 ![guestbook app](assets/guestbook-app.png)
-![view app](assets/guestbook-tree.png)
 
+A panel will be opened and then, click on *Synchronize* button.
+
+You can see more details by clicking at the guestbook application:
+
+![view app](assets/guestbook-tree.png)