Add steps for the 4.1 stage.

Author: jonathanrocher

stage4.1_first_application/README.md

@@ -1 +1,11 @@
 # First real version of the pycasa ETS pyface application!
+Building on the hello world application, this stage creates a real application 
+that allows to navigate the local drive, and open an image file in the central 
+pane. The following steps are taken here: 
+- create a realistic task with a split editor area pane for the central pane 
+  and a file browser dock pane that exposes the home folder using the custom 
+  version of TraitsUI's `FileEditor`. 
+- Adds a ImageFile model, view and an editor so that an image can be open in 
+  the central pane.
+- Add a listener on the file browser double-click event to trigger opening the 
+  image file.