Update and organize readme.

Lombiq.HelpfulExtensions/Extensions/Widgets/Readme.md

@@ -2,9 +2,20 @@
 
 Adds multiple helpful widget content types. These are basic widgets that are added by built-in Orchard Core recipes though in case of using a custom setup recipe these can be added by this feature too.
 
-Includes:
+## ContainerWidget
 
-- ContainerWidget: Works as a container for further widgets. It has a FlowPart attached to it so it can contain additional widgets as well.
-- HtmlWidget: Adds HTML editing and displaying capabilities using a WYSIWYG editor.
-- LiquidWidget: Adds Liquid code editing and rendering capabilities.
-- MenuWidget: Renders a Bootstrap navigation menu as a widget using the provided `MenuItem`s.
+Works as a container for further widgets. It has a FlowPart attached to it so it can contain additional widgets as well.
+
+## HtmlWidget
+
+Adds HTML editing and displaying capabilities using a WYSIWYG editor.
+
+# LiquidWidget
+
+Adds Liquid code editing and rendering capabilities.
+
+# MenuWidget ("Menu Navigation Provider Widget")
+
+Renders a Bootstrap navigation menu as a widget using the provided `MenuItem`s.
+
+> ℹ️ Normally the menu is populated from `INavigationProvider` implementations that create the menu items programmatically. If you use [Lombiq Base Theme for Orchard Core](https://github.com/Lombiq/Orchard-Base-Theme), it has [`MainMenuNavigationProvider`](https://github.com/Lombiq/Orchard-Base-Theme/blob/dev/Lombiq.BaseTheme/Services/MainMenuNavigationProvider.cs). This automatically translates an existing content item with a `MenuItemsListPart` and the `main-menu` alias into compatible navigation, so you can edit menu items from the content editor.