Update overview.md (#392)

I have added an example of column and row being used with expand.

Author: qwerty108109

docs/controls/overview.md

@@ -103,6 +103,27 @@ When a child Control is placed into a [`Column`](/docs/controls/column) or a [`R
 
 For more information and examples about `expand` property see "Expanding children" sections in [`Column`](/docs/controls/column#expanding-children) or [`Row`](/docs/controls/row#expanding-children).
 
+Here is an example of expand being used in action for both [`Column`](/docs/controls/column) and [`Row`](/docs/controls/row) .
+```pyhton
+import flet as ft
+
+
+def main(page: ft.Page):
+    page.spacing=0
+    page.padding=0
+    page.add(
+            ft.Column(controls=[
+              ft.Row(
+                  [
+                  ft.Card(content=ft.Text("Card_1"),color=ft.Colors.ORANGE_300,expand=True,height=page.height,margin=0),
+                  ft.Card(content=ft.Text("Card_2"),color=ft.Colors.GREEN_100,expand=True,height=page.height,margin=0)
+                  ],expand=True,spacing=0),
+                               ],expand=True,spacing=0),
+           )
+
+ft.app(main)
+```
+
 ### `expand_loose`
 
 Effective only if `expand` is `True`.