Update doc

Author: dvoituron

examples/Demo/FluentUI.Demo.Client/Documentation/Components/List/Listbox/FluentListbox.md

@@ -9,6 +9,10 @@ The **FluentListbox** component allows one option to be selected from a list of
 
 ## Default
 
+Find here an example of the default usage of the **FluentListbox** component.
+If an item is selected, the user cannot deselect it. If you want to allow the user to deselect the item,
+you can add an empty item.
+
 {{ ListboxDefault }}
 
 ## Appearance
@@ -26,6 +30,9 @@ Use the **Multiple** parameter to enable multiple selections. Selected items are
 
 ## Disabled and ReadOnly
 
+You can disable the **FluentListbox** component by using the **Disabled** parameter.
+You can make the **FluentListbox** component read-only by using the **ReadOnly** parameter.
+
 {{ ListboxDisabledReadOnly }}
 
 ## Many items