Doc: update External Tools topic

Fix changed UI text. Describe the "Modifies current document"
check box. Update screenshot.

Change-Id: I269d7e07780ddbc42b1eae917022965dbbe113e6
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

doc/src/howto/creator-external-tools.qdoc

@@ -66,7 +66,8 @@
     for viewing and testing while you are developing an application.
 
     To preview the currently active QML file, select \gui Tools > \gui External
-    > \gui {Qt Quick} > \gui {Preview (qmlviewer)} or \gui {Preview (qmlscene)}.
+    > \gui {Qt Quick} > \gui {Qt Quick 1 Preview (qmlviewer)} or
+    \gui {Qt Quick 2 Preview (qmlscene)}.
 
     \section1 Using External Text Editors
 
@@ -127,6 +128,10 @@
         \li In the \gui {Error output pane}, select how to handle error messages
             from the tool.
 
+        \li Select the \gui {Modifies current document} check box to make sure
+            that if the current document is modified by the tool, it is saved
+            before the tool is run and reloaded after the tool finishes.
+
         \li In the \gui Input field, specify text that is passed as standard
             input to the tool.