Show the todo picture in the Readme, and say how it was taken

🤖 Generated with [ECA](https://eca.dev) (anthropic/claude-opus-4-8)

Co-Authored-By: eca-agent <git@eca.dev>

Readme.org

@@ -3,6 +3,10 @@
 Desktop programs in Bjolang, written as a model, a ~gui-update~ and a ~view~,
 and shown with [[https://avaloniaui.net][Avalonia]].
 
+[[file:docs/todo.png]]
+
+The todo list above is [[file:examples/todo.bjo][examples/todo.bjo]].
+
 #+BEGIN_SRC scheme
 (import (bjogui view))
 (import (bjogui app))
@@ -159,6 +163,11 @@ cancelled, and the program ends.
 
 - ~(run-app init gui-update view #:subscriptions #:title #:width #:height)~
   opens a window and runs until it is closed.
+- ~#:screenshot path~ makes ~run-app~ save a PNG of the window once it is
+  shown, at twice its size, and close it. It is the environment variable
+  ~BJOGUI_SCREENSHOT~ unless the program says otherwise, so any program can
+  be pictured with no change: ~BJOGUI_SCREENSHOT=docs/todo.png bjo run
+  examples/todo.bjo~ made the picture above.
 - ~(start-app init gui-update view on-root #:subscriptions)~ makes the controls
   with no window, and gives ~on-root~ the control to show. Its fibers belong
   to the scope it is started in.
@@ -189,6 +198,7 @@ bjo run tests/controls.bjo  # prints "bjogui controls ok"
 bjo run tests/lists.bjo     # prints "bjogui lists ok"
 bjo run examples/counter.bjo
 bjo run examples/stopwatch.bjo
+bjo run examples/todo.bjo
 #+END_SRC
 
 * Not yet