Updated Container API (markdown)

Container-API.md

@@ -108,6 +108,34 @@ of the container unless the container has padding specified.
 
 The **container.PlaceWidget** option places the provided widget into the container.
 
+[[/images/container-api/placed_button.gif|placed_button]]
+
+The following code places a button widget inside a container as shown above:
+
+```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 err
+}
+
+c, err := container.New(
+    t,
+    container.PlaceWidget(b),
+)
+if err != nil {
+    return err
+}
+```
+
 ### Widget alignment options
 
 The following options can be used to align a widget within the container both