Updated Dynamic layout (markdown)

Dynamic-layout.md

@@ -26,4 +26,40 @@ The **Container.Update** method applies the specified options to a container wit
 
 ### Replacing widget in a container
 
+The following code places a button widget inside a container and then updates the container by replacing the button with a Text widget:
+
+```go
+tb, err := termbox.New()
+if err != nil {
+    panic(err)
+}
+defer tb.Close()
+
+b, err := button.New("hello world", func() error {
+    return nil
+},
+)
+if err != nil {
+    return fmt.Errorf("button.New => %v", err)
+}
+
+t, err := text.New()
+if err != nil {
+    return fmt.Errorf("text.New => %v", err)
+}
+
+c, err := container.New(
+    t,
+    container.PlaceWidget(b),
+    container.ID("myID"),
+)
+if err != nil {
+    return fmt.Errorf("container.New => %v", err)
+}
+
+if err := c.Update("myID", container.PlaceWidget(t)); err != nil {
+    return fmt.Errorf("c.Update => %v", err)
+}
+```
+
 ### Changing the layout by specifying new splits