Adding a menu item is very easy, You just have to add an object in the 'routesConfig' array in the 'routesConfig' file (path given in step 1). The Item object should look contain the following properties as shown in the screenshot shown below.
In the nutshell, You just have to add an object in order to array a new menu. The object contains a property named 'type' which can have three values i.e. 'group', 'collapse', and 'item'. You just have to pass the correct value to this 'type' property as per the type of menu you want to add. All other properties in the object remain the same