Doc: Revise document viewer example

Restructure content to follow the application examples template.

Fixes: QTBUG-137896
Pick-to: 6.10
Change-Id: Id94e8e6cc753d4267b3e75bb4f1c136cbd4d699d
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
Reviewed-by: Jerome Pasion <jerome.pasion@qt.io>

examples/demos/documentviewer/doc/src/documentviewer.qdoc

@@ -9,6 +9,8 @@
     \meta {tag} {demo,widgets,mainwindow}
     \brief A Widgets application to display and print JSON, text, and PDF files.
 
+    \image documentviewer_open.png
+           {Document viewer UI showing a 'Select Open Mode' pop-up}
 
     \e{Document Viewer} demonstrates how to use a QMainWindow with static
     and dynamic toolbars, menus, and actions. Additionally, it demonstrates
@@ -22,8 +24,7 @@
         \li Localizing the UI to different languages.
     \endlist
 
-    \image documentviewer_open.png
-
+    \include examples-run.qdocinc
 
     \section1 Creating an application and the main window
 
@@ -38,7 +39,6 @@
     \printuntil exec
     \printline }
 
-
     \section1 MainWindow class
 
     The \c MainWindow class provides an application screen with menus,
@@ -53,7 +53,6 @@
     showing bookmarks and thumbnails. On the right, there is a QScrollArea for
     viewing file content.
 
-
     \section1 ViewerFactory class
 
     The \c ViewerFactory class manages viewers for known file types. These viewers
@@ -95,7 +94,6 @@
     \skipto m_viewer->initViewer
     \printuntil }
 
-
     \section1 AbstractViewer class
 
     \c AbstractViewer provides a generalized API to view, save, and print a
@@ -135,7 +133,6 @@
     This signal notifies the application that a document was successfully
     loaded.
 
-
     \section1 TxtViewer class
 
     \c TxtViewer is a simple text viewer, inheriting from AbstractViewer.
@@ -181,7 +178,6 @@
     Widget Example}. It demonstrates the use of QScroller to smoothly
     flick through a document.
 
-
     \section1 Other relevant classes
 
     \section2 HoverWatcher class
@@ -427,5 +423,7 @@
         \printuntil }
     \endlist
 
+    \section1 Source files
 
+    \sa {All Qt examples}
 */