Tweak description of stage 4.

Author: jonathanrocher

README.md

@@ -101,9 +101,11 @@ are able to reach the end goal.
   - step 1: python script
   - step 2: more robust script with ETS-Traits
   - step 3: GUI: first traitsUI views
-  - step 4: pyface application: tree navigator and double-click on an image to 
-    display the traitsUI view of the image.
-  - INTERLUDE: code structure for scalability
+  - step 4: First pyface application: 
+    - Hello world
+    - INTERLUDE: code structure for scalability
+    - First pycasa: tree navigator to open an image in the central tabbing 
+      system.
   - step 5: Fuller pyface application: 
     - add folder editor to display a table of metadata for all images inside
     - add button to launch the face detection on all images