Updated readme

README.md

@@ -24,6 +24,39 @@ following lines in your HTML code:
 <script src="https://cdn.jsdelivr.net/gh/midstar/jdmenubar/jdmenubar.min.js"></script>
 ```
 
+# Usage
+
+This library consists of the MenuBar object and a css for the design.
+
+The MenuBar object requires the HTML object (typically a DIV element)
+and an array of so called menuItem's. The menuItem's represents each
+element in the menu and its properties. 
+
+Each menuItem object may have following properties:
+
+| Property name | Mandatory | Description                                                                                         |
+|---------------|-----------|-----------------------------------------------------------------------------------------------------|
+| text          | Yes       | The "title" of the menuItem.                                                                        |
+| id            | No        | Identity of item. Only needed if getItemWithId() method will be used for update.                    |
+| handler       | No        | Function (callback) to execute when menuItem is selected.                                           |
+| subMenuItems  | No        | An array of menuItem's for a sub menu. Cannot be combined with handler property.                    |
+| icon          | No        | Left side symbol. Can be text symbol or IMG element. Not allowed for first level of menuItem's.     |
+| shortcut      | No        | Right side text describing the short cut for this action. Not allowed for first level of menuItem's |
+
+A special type of menuItem is the separator which can only be used in a
+sub menu and not in the "top menu". The separator shall only have one
+property, separator, which shall be to true.
+
+The list of menuItems might be updated after the menu bar has been
+generated, but to make the changes have effect the update() method
+in the MenuBar object needs to be called.
+
+To simplify update of individual menuItems each menuItem can be
+given an identity (with the id property) and be fetched and updated
+with the getItemWithId() method.
+
 # How to customize the look-and-feel
 
-Checkout example_customized.html
+The jdmenubar.css style sheet includes a number of variables to 
+customize colors and sizes. See the customized example
+[source](https://github.com/midstar/jdmenubar/blob/main/example_customized.html).