Doc: Describe running apps from the Application Output pane

This saves time when developing Qt Quick applications, because
the QML files are interpreted at runtime. Therefore the
app does not need to be recompiled if only QML files changed.

Update the screenshot to make the Run button more visible.

Change-Id: I0ff2a1ca0fc24102e9c87b00896c387c18d0f1f1
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

doc/src/projects/creator-projects-running.qdoc

@@ -61,6 +61,17 @@
 
     \endlist
 
+    The \uicontrol {Application Output} pane displays the status of the
+    application while it is running. You can select the \uicontrol Run button
+    in the pane to re-run applications without building them first. This is
+    useful when developing Qt Quick applications, because the QML files are
+    interpreted at runtime. Therefore, the application does not need to be
+    built again if you edited only QML files. This saves time especially if
+    the application contains large image files that would need to be bundled
+    into the resource file before running the application.
+
+    \image qtcreator-application-output.png
+
     For more information on the options you have, see
     \l{Specifying Run Settings}.