Update theming snippet in Overview docs

- merge the xmlns declarations into the single ThemeBehavior XAML snippet
- drop the separate note block per PR review feedback

Author: sergepilipchuk

CS/CodeEditor/Docs/Overview.md

@@ -120,6 +120,12 @@ By default, `CodeEditor` does not automatically track DevExpress theme changes.
 To synchronize Monaco with the active DevExpress theme, attach `ThemeBehavior`:
 
 ```xml
+xmlns:ce="clr-namespace:CodeEditor;assembly=CodeEditor"
+xmlns:cet="clr-namespace:CodeEditor.Theming;assembly=CodeEditor"
+xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
+
+...
+
 <ce:CodeEditor
     Text="{Binding Code}"
     EditorLanguage="csharp">
@@ -131,14 +137,6 @@ To synchronize Monaco with the active DevExpress theme, attach `ThemeBehavior`:
 </ce:CodeEditor>
 ```
 
-> **Note:** Declare the namespace prefixes used above on the root element of your view (as in the Quick Start):
-
-```xml
-xmlns:ce="clr-namespace:CodeEditor;assembly=CodeEditor"
-xmlns:cet="clr-namespace:CodeEditor.Theming;assembly=CodeEditor"
-xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
-```
-
 `ThemeBehavior`:
 
 - Detects the current DevExpress theme