Documentation added

README.md

@@ -10,7 +10,7 @@ The package exports one procedure:
 
 (rkdt "notes.rkt")
 ```
- 
+
 By default `rkdt` shows the editor and returns immediately. Use `#:wait? #t`
 when execution should continue only after the editor is closed:
 
@@ -22,7 +22,12 @@ The initial window geometry can be specified with `#:width`, `#:height`, `#:x`,
 and `#:y`. Window positions and sizes are remembered per internal editor number
 and per screen configuration.
 
-The frame can be customized with `#:frame-cb`. For example:
+The frame can be observed or customized with `#:frame-cb`. The callback receives
+an event symbol and the editor frame. It is called at the lifecycle points
+`'before-show`, `'after-show`, `'wait-for-close`, and `'on-close`.
+`'wait-for-close` is emitted only when `#:wait? #t` is used.
+
+For example, the window title can be changed before the frame becomes visible:
 
 ```racket
 (require racket/class
@@ -30,8 +35,9 @@ The frame can be customized with `#:frame-cb`. For example:
 
 (rkdt "notes.rkt"
       #:frame-cb
-      (λ (frame)
-        (send frame set-label "Notes")))
+      (λ (event frame)
+        (when (eq? event 'before-show)
+          (send frame set-label "Notes"))))
 ```
 
 The standard File menu does not contain the Exit/Quit command, so closing one