Doc: Open Documents option in the Advanced Search pane

Change-Id: Ibede904f49905d0840051783f233ef290436cf14
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

doc/src/editors/creator-editors.qdoc

@@ -1305,8 +1305,7 @@
 
     \section1 Advanced Search
 
-    To search through projects, files on a file system or the currently open
-    file:
+    To search through projects, files on a file system or currently open files:
 
     \list 1
 
@@ -1334,6 +1333,8 @@
 
                 \li \gui{Current File} searches only the current file.
 
+                \li \gui {Open Documents} searches all open files.
+
             \endlist
 
         \li Enter the text you are looking for and click \gui Search.